Church, et.al., 2013. “Sea change: Charting the course for biogeochemical ocean time-series ...

14 Pages·2013·3.47 MB·English

by  Matthew J. Church

Deep-SeaResearchII93(2013)2–15
ContentslistsavailableatSciVerseScienceDirect
Deep-Sea Research II
journal homepage: www.elsevier.com/locate/dsr2
Sea change: Charting the course for biogeochemical ocean time-series
research in a new millennium
Matthew J. Churcha,n, Michael W. Lomasb, Frank Muller-Kargerc
aDepartmentofOceanography,UniversityofHawaii,1000PopeRoad,Honolulu,HI96822,UnitedStates
bBigelowLaboratoryforOceanSciences,60BigelowDrive,EastBoothbay,ME04544,UnitedStates
cInstituteforMarineRemoteSensing,CollegeofMarineScience,UniversityofSouthFlorida,St.Petersburg,FL33701,UnitedStates
a r t i c l e i n f o a b s t r a c t
Availableonline31January2013 Ocean time-series provide vital information needed for assessing ecosystem change. This paper
summarizesthehistoricalcontext,majorprogramobjectives,andfutureresearchprioritiesforthree
Keywords:
Time-series contemporaryoceantime-seriesprograms:TheHawaiiOceanTime-series(HOT),theBermudaAtlantic
Oceanbiogeochemistry Time-series Study (BATS), and the CARIACO Ocean Time-Series. These three programs operate in
HOT physicallyandbiogeochemicallydistinctregionsoftheworld’soceans,withHOTandBATSlocatedin
BATS theopen-oceanwatersofthesubtropicalNorthPacificandNorthAtlantic,respectively,andCARIACO
CARIACO situatedintheanoxicCariacoBasinofthetropicalAtlantic.Allthreeprogramssustainnear-monthly
Carboncycling shipboard occupations of their field sampling sites, with HOT and BATS beginning in 1988, and
CARIACO initiated in 1996. The resulting data provide some of the only multi-disciplinary, decadal-
scaledeterminationsoftime-varyingecosystemchangeintheglobalocean.Facilitatedbyascoping
workshop(September2010)sponsoredbytheOceanCarbonBiogeochemistry(OCB)program,leaders
ofthesetime-seriesprogramssoughtcommunityinputonexistingprogramstrengthsandforfuture
researchdirections.Themesthatemergedfromthesediscussionsincluded:
1. Shipboard time-series programs are key to informing our understanding of the connectivity
betweenchangesinocean-climateandbiogeochemistry.
2. The scientific and logistical support provided by shipboard time-series programs forms the
backbonefornumerousresearchandeducationprograms.Futurestudiesshouldbeencouragedthat
seekmechanisticunderstandingofecologicalinteractionsunderlyingthebiogeochemicaldynamics
atthesesites.
3.Detectingtime-varyingtrendsinoceanpropertiesandprocessesrequiresconsistent,high-quality
measurements. Time-series must carefully document analytical procedures and, where possible,
tracetheaccuracyofanalysestocertifiedstandardsandinternalreferencematerials.
4.Leveragedimplementation,testing,andvalidationofautonomousandremoteobservingtechnologies
attime-seriessitesprovidenewinsightsintospatiotemporalvariabilityunderlyingecosystemchanges.
5.Thevalueofexistingtime-seriesdataforformulatingandvalidatingecosystemmodelsshouldbe
promoted.
In summary, the scientific underpinnings of ocean time-series programs remain as strong and
importanttodayaswhentheseprogramswereinitiated.Theemergingdatainformourknowledgeof
theocean’sbiogeochemistryandecology,andimproveourpredictivecapacityaboutplanetarychange.
&2013ElsevierLtd.Allrightsreserved.
1. Preface play interactive roles in shaping climate, serve as reactive pools of
bioelements, and comprise vast reservoirs of biodiversity. Despite
1.1. Time,water,andchange theirimportancetohumansandplanetaryhealth,wecurrentlylack
confidentpredictiveunderstandingofhowoceanicecosystemsmay
Oceans are vital to Earth’s habitability and are important socio- respond to global change. In part this derives from chronic under-
economic resources. The massive and diverse oceanic ecosystems sampling of these remote and spatiotemporally complex habitats.
There are currently only a few regions in the sea where we have
sustained, decadal-scale observations on the interactions between
ocean biogeochemistry, hydrography, and ecology. These few time-
nCorrespondingauthor.
E-mailaddress:[email protected](M.J.Church). series, built largely around shipboard sampling programs, provide
0967-0645/$-seefrontmatter&2013ElsevierLtd.Allrightsreserved.
http://dx.doi.org/10.1016/j.dsr2.2013.01.035
M.J.Churchetal./Deep-SeaResearchII93(2013)2–15 3
evidencethatocean–climate–humaninteractionscanhavecascading Time-series (HOT), Bermuda Atlantic Time-series Study (BATS), and
impacts on ecosystem processes across a wide range of time and theCARIACOOceanTime-Series.Alltheseprogramsmaintainnear-
spacescales.Moreover,thesetime-seriesrecordsprovidethecritical monthly ship-based sampling programs in hydrographically and
data needed to better understand the ocean’s and our planet’s biogeochemicallydistinctregions:theNorthPacificSubtropicalGyre
sensitivitytochange. (NPSG),thesubtropicalNorthAtlantic,andtheCariacoBasininthe
A major challenge facing ocean scientists is how to advance tropical North Atlantic, respectively (Table 1). These sites are com-
interdisciplinary, multi-decadal time-series programs that provide plementedbysystematicobservationscollectedfromotherobserving
highqualitydataatsufficientspatiotemporalresolutiontoinformour platformsincludingmoorings,satellites,floats,andgliders.Thedata
understandingofmarineecosystemchange.Despitethesuccessesof fromthesetime-seriesprogramsprovidesomeoftheonlydecadal-
ship-basedtime-seriesindocumentingoceanchange,samplingfrom scale records available for assessing seasonal- to interannual-scale
researchvesselsisrelativelyrestrictiveinitsspatio-temporalresolu- changes in ocean hydrographic structure, biogeochemistry, and
tion. Rising costs associated with operating and maintaining ships biology.
require continual reassessment and justification of the cost–benefit Oceanbiogeochemistrytime-seriesprogramsremainvitalcom-
scenariostoscienceandsocietybehindsustainingship-basedocea- munity resources, providing invaluable cross-disciplinary informa-
nographic programs. Moreover, technology advances in the past tion on ocean ecosystem change. Discussions as part of this
decade now allow for high-resolution autonomous sampling of workshopprovidedanopportunityforcommunityinputonscience
variousoceanographicproperties.Suchfactorshavepartlymotivated priorities for the next decade of research at these sites, including
the current expansion of ocean observational systems designed to exploringthestrengthsandlimitationsofexistingshipboardtime-
relyonremoteandautonomoussensingplatforms,promisinghigher series programs. In this paper, we summarize some of these
frequencyspatio-temporalsamplingofecosystemdynamicsdifficult discussionswithintheframeworkoftheresearchdoneatthethree
to adequately sample from ships alone, at a potential cost savings. on-going time-series, define opportunities for new science built
Satellites, floats, gliders, moorings, and remotely operated vehicles around these programs, and provide several recommendations for
have all become increasingly central to such observing strategies. improvingthestateofglobaloceanobservingthatincludesalong-
However,todate,welackthecapabilitiestodetectmanyofthekey termroleforshipboardtime-seriesresearch.
climate-sensitivebiogeochemicalpropertiesandprocessesweknow
are fundamental to ecosystem function from these autonomous
sensingplatforms.Balancinginvestmentsrequiredtomaintaincom- 2. Background
prehensiveoceancarbonandbiogeochemistrytime-seriesandmore
autonomousobservatorysystemsiscentraltotheevolvingvisionof 2.1. Ifyoubuildit,theywillcome
theoceansciences.
FacilitatedbytheOceanCarbonBiogeochemistry(OCB)program, Thevisiontoestablishshipboardtime-seriessprungfromrecogni-
threecontemporaryoceantime-seriesprogramsconveneda‘‘scoping tionthatdetectinghowanthropogenicandnatural-climatechanges
workshop’’ in September 2010 to gather community input on the influence the biosphere is impossible without time-resolving mea-
future direction and scope of ship-based time-series programs. The surementscollectedoverlongperiodsoftime(Keelingetal.,1995;
workshop largely focused on three on-going programs whose Likensetal.,1996;Schindler,1988).Historicalrootsforcontemporary
researchalignswiththeOCBprogramobjectives:theHawaiiOcean ocean time-series can be traced in part to use of weather ships,
Table1
OceanCarbonBiogeochemistrytime-seriesprogramsandstudysitecharacteristics.
Programand Periodand Generalsite Annualmean(and Samplinginfrastructure Programleadership
studysite frequencyof characteristics range)primary
shipboard productivityand
observations carbonexport
(molCm(cid:2)2yr(cid:2)1)
BATS 1988–present SubtropicalNorthAtlantic 14(9.7–16), Shipboardobservations AnthonyKnap(1988–2012),Anthony
(31.751N, (monthly) (SargassoSea),seasonally 0.87(0.67–1.1) (1988–present),bottom- Michaels(1989–1996),RobJohnson
64.161W) oligotrophic,moderate mooredsedimenttraps (1988–present),NickBates
seasonality(largely (1978–present), (1995–present),DebbieSteinberg(1997–
attributable profilingfloats(2009– 2001),CraigCarlson
towintermixing) present), (1992–2001),MichaelLomas
mooredplatform(1994– (2001–present)
2007)
HOT—Station 1988–present SubtropicalNorthPacific, 14(9.4–18), Shipboardobservations DavidKarl,RogerLukas,RicardoLetelier,
ALOHA (monthly) persistentlyoligotrophic, 0.84(0.64–1.2) (1988–present),bottom- JohnDore,RobertBidigare(all1988–
(22.751N, lowseasonalityin mooredsedimenttraps present),EricFiring
1581W) hydrography (1992–present), (1988–1998),StephenChiswell(1988–
andbiogeochemistry profilingfloats(2005– 1993),ChristopherWinn(1988–1997),
present), MichaelLandry
mooredplatforms(1997– (1992–present),LuisTupas
present),cabledobservatory (1991–2000),DaleHebel
(2010–present) (1988–2005),MatthewChurch(2009–
present)
CARIACO 1995–present TropicalCaribbeanSea 40(29–53),2.1 Shipboardobservations FrankMuller-Karger,MaryScranton,
(10.51N, (monthly) (CariacoBasin),mesotrophic, (1.4–2.8) (1995–present),bottom- GordonTaylor,RobertThunell,Ramon
64.671W) highlyseasonalhydrography mooredsedimenttraps Varela,YreneAstor
andbiogeochemistry (1995–present) (all1995–present),KentFanning,Luis
(attributabletochangesin Troccoli(2000–present),BaumarMarı´n
upwelling) (2000–present),RobertWeisberg(1996–
2006),
JohnJ.Walsh(1995–2000)
4 M.J.Churchetal./Deep-SeaResearchII93(2013)2–15
deployedinremoteregionsoftheworld’soceanstogathermeteor- forcing of ocean physics, and with the support from the Office of
ological data necessary to improve weather forecast models. NavalResearch,HenryStommel(WoodsHoleOceanographyInstitu-
The value of such repeated occupations to otherwise inaccessible tion) and William Sutcliffe (Bermuda Biological Station) initiated a
regions of the oceans attracted the interests of a diverse group of biweeklysamplingcampaigntophysicallycharacterizethe(cid:3)2600m
scientists.The‘‘ancillary’’observationscollectedbyprocess-oriented water column at Hydrostation S in the northwestern Sargasso Sea
scientific programs, conducted alongside the weather-ship hydro- (Jenkins,1982;Schroederetal.,1959).Providingphysicalcontextand
graphic and meteorological sampling, led to important discoveries. regular access to the open sea, facilitated in large part by suitably
Forexample,oceanproductivityandirradiancemeasurementsat equipped research vessels and infrastructure support from the
Weathership ‘‘M’’ in the North Sea laid the framework for the Bermuda Biological Station, Hydrostation S rapidly attracted new
formulationofthecriticaldepththeoryexplainingtheprerequisite anddiversifiedscienceprograms.Amongthefirsttocapitalizeonthe
interactionsbetweenlight,mixing,andphotosynthesisincontrol- HydrostationStime-serieswereWoodsHolescientistsDavidMenzel
ling formation of phytoplankton blooms (Sverdrup, 1953). The and John Ryther. By placing measurements of productivity and
legacyoftheseprogramscontinuestoday.Forexample,measure- nutrientcyclingintothetime-resolvedhydrographiccontextafforded
mentsconductedatStationP(501N,1451W)continuethe obser- byHydrostationS,theirworkhelpeddefinefactorsshapingbiogeo-
vations started in the 1940s from a weather-ship outpost in the chemistryinthesubtropicaloceangyres(MenzelandRyther,1960,
subarctic North Pacific (Freeland, 2007; Whitney and Tortell, 1961). By the 1970s and 1980s several important biogeochemical
2006). The resulting data highlight complex, climate-forced bio- studies had coalesced around the HydrostationS, including a study
geochemical interactions, including long-term changes in dis- that continues today aimed at quantifying temporal relationships
solved oxygen concentrations within the main thermocline of betweenupper-oceanproductivityandthedownwardfluxofmate-
theNorthPacificOcean(Whitneyetal.,2007). rialtothedeepsea(Conteetal.,2001;DeuserandRoss,1980;Deuser
In addition to ocean weather ships, economic interests in et al., 1983, 1990), and geochemical approaches to estimate net
commercially important fisheries motivated the establishment of communityproductivity(Jenkins,1982;JenkinsandGoldman,1985).
time-seriesmonitoringprograms.ThecollapseofthePacificsardine Thesestudiesrevealedthatthevastsubtropicaloceangyresserveas
fishery in the mid 1940s resulted in the creation of the California globally important carbon reactors, where productivity was greater
Cooperative Fisheries Investigations Program (CalCoFI) program in than historically recognized and whose carbon storage potential
1949. This program has maintained a near-continuous record of depended on complex biological–physical couplings. By embedding
climaticinfluencesonecosystemvariabilityintheCaliforniaCurrent suchmeasurementsintothetime-resolvinghydrographicframework,
ecosystem (Field et al., 2006; Rebstock, 2002; Rykaczewski and Hydrostation S became one of the few places in the world where
Checkley,2008)withafocusonfisheriesstocksandmanagement. quantitativeinformationonseasonaltointerannualscaleinteractions
The establishment of Hydrostation S (321100N, 641300E) off Ber- betweenplanktonecology,hydrographicforcing,andbiogeochemical
mudain1954marksamajorhistoricalentrypointformodernocean cyclesintheopenseawasavailable.
time-series research (Fig. 1). Motivated by the desire to better These early efforts solidified a recurrent theme among con-
understand seasonal to interannual variability in meteorological temporary ocean time-series: regular access to the open sea
Fig.1. Timelineofresearchconductedatvariousoceantime-seriessitesaroundtheglobe.Coloredlinesindicatetypesofsamplingandmeasurementactivities(ships,
moorings,gliders,floats,andsedimenttraps).Solidlinesreflectsustainedmeasurementprogramonatleastmonthlytimescales;dashedlinesindicatemeasurements
havecontinuedbutatlowerthanmonthlyfrequency;andgapsintime-seriesrecordsareshownbybrokenlines.Siteabbreviationsare:StationS,HydrostationS;OSP,
OceanStationPapa;Pal.LTER,PalmerLongTermEcologicalResearchprograminAntarctica.FigureadaptedfromKarletal.(2003).(Forinterpretationofthereferencesto
colorinthisfigurecaption,thereaderisreferredtothewebversionofthisarticle.)
M.J.Churchetal./Deep-SeaResearchII93(2013)2–15 5
afforded by a ship provides unique opportunities for studying initiated with support from the Venezuelan government, NSF, and
oceanprocesses,developingnewmethods,trainingstudentsand NASA. The project seeks to examine linkages between upper ocean
technicians, and testing hypotheses. Encapsulating these attri- productivity,terrigenousmaterialinputtotheenclosedbasin,mate-
butesinarichhistoricalcontextofphysicalandbiogeochemical rial fluxes from the shelf into deep water, and the preservation of
measurements further strengthens the allure of such programs. climate signals in the sediment accumulating at the bottom of this
These efforts inspired questions that remain at the core of anoxic tropical ecosystem (Muller-Karger et al., 2010; Taylor et al.,
contemporaryoceanography,includingidentifyingprocessescon- 2012).Theregionhasarichhistoryofpaleo-oceanographicresearch
trolling rates of primary production; examining how plankton (Black et al., 1999; Hughen et al., 2004) that provides additional
communitystructureinfluencesproductivityandmaterialexport; motivationforcontemporarytime-seriesstudieslinkingupperocean
quantifying nutrient supply to the upper ocean; and defining biogeochemical processes to climate signals stored in seafloor
seasonal to interannual scale variability in stocks of oxygen, sediments.
carbon, and nutrients essential for life on Earth. The time-series Thesuccessesofthetime-seriesprogramsmadethemamong
sampling approach allows studying ecosystem behavior that themosttransformativeaccomplishmentsofJGOFS.Bytheendof
wouldbeotherwiseobscuredbyhigherfrequency‘‘noise’’ortime the JGOFS program in the early 2000s, HOT, BATS, and CARIACO
lagsbetweenperturbationsandresponses(Magnuson,1990). found themselves lacking a unified programmatic base to facil-
The scientific and logistical successes of these early studies itate exchange of ideas on science priorities pursued by these
stimulatedrecognitionthatoceanecosystemspreviouslyconsidered programs.Theinitiationof theOCBprogramin2007 provideda
toberelativelystaticexhibitsignificanttemporalvariabilityovera scientific support framework whose research interests aligned
varietyofscales.Moreover,theseprogramshighlightedthatefforts well with these on-going time-series efforts. HOT, BATS, and
todocumentchangestothesearequireawell-formulatedplanfor CARIACO remain focused on studying processes that control the
sustained, long-term ocean time-series research. By 1984, ocean distributions and cycling of elements in the sea, with specific
scientistsworkingundertheumbrellaoftheScientificCommitteeof focus on carbon, in sufficientdetail to provide predictiveunder-
OceanicResearch(SCOR)formulatedplansforanewoceanographic standing on how global scale perturbations to ocean-climate
programtodocumentanthropogenicallyinducedchangestothesea. might influence biogeochemical transformations and feedbacks.
TheGlobalOceanFluxStudy(GOFS)soughtbetterunderstandingof Toachievethisbroadobjective,theprogramsseekunderstanding
the processes controlling ocean biogeochemistry at regional to ofthefollowing:
global scales (Global Ocean Flux Study, 1984). With international
partnerships in place, the Joint Global Ocean Flux Study (JGOFS)
emerged as one of the first core projects of the International 1) The linkages between seasonal, interannual, and long-term
Geosphere-Biosphere Program (IGBP). Central to the objectives of (multi-decadal)variabilityandtrendsinoceanphysics,chem-
JGOFSwastheneedtodeterminetheinteractionsamongelemental istry,andbiology.
cycles in the sea and understand the processes controlling time- 2) Processes underlying physical and biogeochemical temporal
varying fluxes of carbon and associated bioelements. Ocean time- variability.
series were included as an essential component of this interdisci- 3) Theroleofphysicalforcingoncarbonfluxes,includingratesof
plinaryprogram(Brewer,2003).AtthesametimethatJGOFSwas biologically mediated carbon transformations, air–sea CO
2
formulatingitsscienceagenda,theWorldClimateResearchProgram exchange,andcarbonexport.
(WCRP) was developing plans for the World Ocean Circulation 4) The response of ocean ecosystems and biogeochemistry to
Experiment (WOCE), a program centered on observations and planetarychange.
models of ocean-climate change. The programs collectively recog-
nizedtheneedforanintegrated,interdisciplinaryapproachtoocean
observing that included relying on time-series sampling. In 1987, Thescientificandlogisticalsupportaffordedbytheseprograms
three separate proposals (two to JGOFS and one to WOCE) were continues to generate activities that serve as focal points for new
submitted to the US National Science Foundation (NSF) for the science,education,andpublicoutreach.Thetimes-seriessiteshave
establishmentofHOTandBATS.StartinginOctober1988bothHOT proven fertile grounds for improving existing methodologies and
and BATS were in the water, undertakingnear-monthly shipboard implementing novel sea sensing technologies (Fig. 1). The short
time-series sampling in the NPSG and Sargasso Sea, respectively duration (o1 week) cruises in globally significant but remote
(KarlandMichaels,1996;MichaelsandKnap,1996). habitatscontinuestoattracttheinterestsofdiversescienceprojects
HOT and BATS were born from the idea that time-series are thatbenefitfromatime-resolvedsamplingapproach.Thecoretime-
essentialtounderstandtime-varyingfluxesofcarbonandassociated seriesbenefitfromtheknowledgeofecosystemdynamicsprovided
vitalelementsintheoceans.ThecoreelementsofbothHOTandBATS by such ancillary research projects, while the ancillary projects
fellundertheauspicesofJGOFSandWOCEthroughoutthelifetimes benefit from time-resolved scientific context and logistical, infra-
of these larger programs. The time-resolved physical and biogeo- structural, and technical support provided by the core programs.
chemical context and regular access to the open sea stimulated As a result, HOT, BATS, and CARIACO have attracted numerous
numerous‘‘ancillary’’researchprojectsthatcontinuetocollectawide scientists,students,teachers,andvolunteersfromallovertheworld
range of observations at both locations. Within 5 years it became seekingopportunitiestoparticipateintime-seriesresearchorjustto
apparentthatoneofthemajorstrengthsoftheseprogramswasthe experience science from aboard a research vessel. Between 1988
interdisciplinary,multi-investigatorapproachtostudyingecosystem and 2009, more than 320 scientists and their staff have been
dynamics. The resulting high-quality measurements, together with involved in process studies that build on the ‘‘core’’ time-series
the scientific and ship-based infrastructure fueled numerous colla- programs,andanadditional 4140‘‘core’’time-seriesscientistsand
borativescientificinteractions.Betweenthelate1980sandthemid- staffhaveparticipatedinHOT,BATS,andCARIACOcruises.Over420
1990s, many time-series programs were initiated in various undergraduate and graduate students and (cid:3)50 teachers
marine ecosystems around the globe (Fig. 1) including Monterey (elementary to university level) from around the globe have and
Bay(MBARI,361430N,1221240W;1989–present),intheMediterra- continue to participate in these cruises for education and training
nean (DYFAMED, 431250N, 71 520E; 1991–present), in the northeast opportunities.Theseprogramshavebecomemodelsbywhichother
Atlantic(ESTOC,291100N,151300W;1994–present),andinthesemi- nationsaredevelopingtheirowntime-seriesprogramstoassistin
enclosed Cariaco Basin (CARIACO; 1995–present). CARIACO was understanding local ecosystems and responses to impacts and
6 M.J.Churchetal./Deep-SeaResearchII93(2013)2–15
change, and which will ultimately help us to understand global- hydrographic, biogeochemical, and ecological characteristics at HOT
scaleoceanchange. and BATS, and both sites experience variability in upper-ocean
dynamicsthatalterbiogeochemicaldynamicsandplanktoncommu-
nity structure across a range of time scales. BATS features higher-
3. Programhighlights salinity waters from the surface to the ocean bottom, compared to
thosefoundatHOT(Fig.2).Moreover,themid-anddeepwatersat
3.1. Fromthepredictabletotheunexpected HOT (41000m) have depleted concentrations of dissolved oxygen
and enriched concentrations of nutrients compared to BATS, both
Allthreetime-seriesprogramsmeasureacoresetofphysicaland signatures consistent with greater time-integrated organic matter
biogeochemicalpropertiesoneachcruise(http://hahana.soest.hawaii. remineralization characteristic of older deep waters in the North
edu/hot/; http://bats.bios.edu/; http://www.imars.usf.edu/CAR/index. Pacific(Fig.2).
html);thesemeasurementswereselectedtoprovideacomprehen- The physical and biogeochemical characteristics of CARIACO
sive and interdisciplinary framework from which to view contrastthoseobservedatHOTandBATS(Fig.2).WhileHOTand
time-varying changes in these oceanic ecosystems. The long list of BATS both sample deep-ocean locations (44700m), CARIACO
highlights emerging from the time-series data records include doc- lies on a geological fracture on the continental shelf (bottom
umentationofprogressivechangesinoceaniccarboninventoriesand depth (cid:3)1400m) off the coast of Venezuela in an permanently
fluxes(Astoretal.,2005,2013;Bates,2001,2007;Doreetal.,2003, anoxicbasin.Thephysicalandbiogeochemicalconditionsatthis
2009; Keeling et al., 2004); unexpected variability in the elemental site are defined by factors influencing oceanography of the
stoichiometryofseawaternutrientpools(Karl,2002;Michaelsetal., tropical and subtropical Atlantic, the Caribbean Sea, and the
1994,1996;Thunelletal.,2008);complexclimate-linkedinteractions continental margin. High near-surface biological productivity
betweenplanktonecologyandbiogeochemistry(Cornoetal.,2007; and settling particulate organic matter flux leads to anoxic
Karl, 1999; Lomas et al., 2010; Taylor et al., 2012); elucidation subsurfacewatersintheCariacoBasin.CARIACOisamesotrophic
of variability associated with pools and fluxes of organic matter tropical ecosystem that experiences seasonally dynamic trade-
(Carlson et al., 1994; Emerson et al., 1997); and the importance of wind forced upwelling (January through May), and episodic
plankton community structure in controlling time-variability in delivery of terrestrially derived organic matter in the autumn
carbonsequestration(Dore etal.,2002;Lomasetal.,2009;Thunell (Hoetal.,2004).Anoxiabelowapproximately250miscausedby
etal.,2007). physical isolation of the deep waters in the basin and the
Onthesurface,HOTandBATSsamplesimilaroceanhabitats:both relatively high biological activity. The lack of oxygen in this
sites are located in relatively warm and isolated subtropical regionofthewatercolumn(4250m)promotesfinelystructured
gyres where Ekman downwelling associated with the anticyclonic verticalredoxgradients(Scrantonetal.,2001;Tayloretal.,2001),
rotationofthegyresresultsindeeppermanentpycnoclinesandnear- includingcompleteremovalofnitratebydenitrification.
surfaceoceanchlorophyllconcentrationsarepersistentlylow(Fig.2). HOT, BATS, and CARIACO all rely on near-monthly ship-
Despitethesebroadsimilarities,therearefundamentaldifferencesin boardsampling.Theresultingtime-seriesdatacaptureseasonally
Fig.2. StudylocationsofHOT(redcircle),BATS(bluediamond),andCARIACO(greentriangle)superimposedover6-yearcompositeofsatellite-derivednear-surfaceocean
chlorophyllconcentrations.Bottompanelsdepicttemperature–salinityrelationships,andverticalprofilesofdissolvedoxygenandnitrateþnitritefromthethreetime-
seriessites.SatellitedatacourtesyoftheOceanBiologyProgram(NASAGoddardSpaceFlightCenter).(Forinterpretationofthereferencestocolorinthisfigurecaption,
thereaderisreferredtothewebversionofthisarticle.)
M.J.Churchetal./Deep-SeaResearchII93(2013)2–15 7
recurringpatternsinbothhydrographicforcingandbiogeochem- decrease to levels similar to those measured at HOT during the
ical dynamics, withboth higher-and lower-frequencyvariability warm,stratifiedsummermonths(Fig.3).Nutrientconcentrations
superimposedon that seasonaldynamic. Although allthree sites inthenear-surfacewatersatCARIACOaretypicallyrelativelylow,
undergo relatively weak seasonal variability in sea surface tem- withNO3(cid:2)þNO2(cid:2) generally o1mM(Astoretal.,2003);however,
peratures (SST), the amplitude and timing of SST variations at the strong vertical gradient in nutrient concentrations, together
BATS are notably different than observed at HOT or CARIACO. with seasonal upwelling, yields upper ocean (0–100m) nutrient
Near-surface ocean temperatures at HOT generally vary o51C inventories that are several hundred times greater than those
over the course of the year, while SST at CARIACO varies about observedatHOTorBATS(Fig.3).
5–81C, and at BATS SST can vary by 491C (Fig. 3). All three Ratesofprimaryproduction(asestimatedfrom14C-bicarbonate
regionsalsodemonstrateseasonalityinthedepthofupperocean assimilation) and particulate matter export at all three sites
mixing. ThemixedlayeratHOTandCARIACOdisplays relatively demonstrate variability on seasonal to interannual scales
weakseasonality(Fig.3);atHOTthemixedlayerisalmostalways (Figs. 4 and 5). Both production and export (and hence rates of
restrictedtotheupper120m(andhencewithintheeuphoticzone newproduction)aresensitivetochangesinplanktoncommunity
(cid:3)125m; Letelier et al., 2004) and at CARIACO the perennially structure and to interannual variations in hydrographic forcing
warmandsalineupperoceanwatersrestrictsmixingto o50m, (Chavezetal.,2011;Cornoetal.,2007;Letelieretal.,1996;Muller-
whichisoftheorderoftheeuphoticzonedepth(Lorenzonietal., Karger et al., 2001; Saba et al., 2010). Moreover, the emerging
2011).Incontrast,mixed-layerdepthsatBATScanexceed400m seasonalclimatologiesinproductionandparticulatecarbonexport
inthelatewinter(andthuscanseasonallyexceedthedepthofthe at these sites highlights several patterns reflective of the unique
euphoticzone (cid:3)100m;Siegeletal.,2001),thenshoalrapidlyto biological responses to annually recurring ecosystem dynamics
o30mbythelatespringandsummer(Fig.3). (Fig.4).Consistentwiththerelativelyquiescentphysicalnatureof
These seasonal differences in hydrographic forcing imprint the NPSG, primary production (0–100m) at HOT typically varies
unique biogeochemical signatures on each region. The relatively (cid:3)2-foldover theyear((cid:3)30and50mmolCm(cid:2)2d(cid:2)1)(Fig. 5). A
weak seasonal mixing combined with rapid plankton growth weak but predictable seasonal dynamic is observed where rates
results in an upper ocean at HOT that is consistently starved of increaseduring the summerwhen irradiance ismaximaland the
nutrients.Depth-integrated(0–100m)inventoriesofNO(cid:2)þNO(cid:2) upper ocean is well stratified. Particulate matter flux (150m)
3 2
at HOT are low throughout the year (Fig. 3), but become more increases o2-foldduringthemoreproductivespringandsummer
variable during the winter periods when mixed-layer depths months (Fig. 5), resulting in a weak seasonal-scale coupling
increaseandincidentirradiancereachesitsannualminima(Karl betweenproductivityandexport.Incontrast,upper-oceanproduc-
etal.,2008;Letelieretal.,2004).Incontrast,nutrientinventories tivity(0–100m)andexport(150m)atBATSincreaseintheearly
atBATSshowmoreprominentseasonality(Steinbergetal.,2001); spring when nutrient inventories are at their annual maximum.
upperocean(0–100m)NO(cid:2)þNO(cid:2) concentrationsincreaseshar- The amplitude of the seasonal cycle in productivity at BATS is
3 2
ply during periods of late winter mixing, and then rapidly largerthanobservedatHOT,withprimaryproductionduringthe
Fig.3. Meanmonthlyseasurfacetemperatures,mixed-layerdepths,anddepth-integrated,upperocean(0–100m)inventoriesofnitrateþnitriteatHOT,BATS,and
CARIACO.Symbolsrepresentmonthlymeans,errorbarsarestandarddeviationsofthemonthlymeans.
8 M.J.Churchetal./Deep-SeaResearchII93(2013)2–15
Fig.4. Time-seriesdeterminationsofnetprimaryproduction(0–100mdepth-integratedrates)andparticulatecarbonexportatHOT(red),BATS(blue),andCARIACO
(green).NotethatcarbonexportatHOTandBATSweremeasuredbyparticleinterceptortrapsat150m;fluxesatCARIACOweredeterminedusingbottommoored
sedimenttrapcollectionsat225m.Solidlinesdepictmeanproductivityorexportforthetime-series;dashedlinesrepresent7onestandarddeviationofthemeanfluxes.
NoteY-axesscalesdifferforCARIACOdata.(Forinterpretationofthereferencestocolorinthisfigurecaption,thereaderisreferredtothewebversionofthisarticle.)
spring bloom periods sometimes 480mmol C m(cid:2)2 d(cid:2)1. By late relativelystrongseasonalityinupperoceanproductivityseason-
spring and early summer production decreases sharply, often alityinparticleexportislesswelldefinedthanateitherHOTor
remaining o30mmolCm(cid:2)2d(cid:2)1throughoutthesummerandfall BATS(Fig.5).
(Fig.5).Despitenotableseasonaldifferencesinupper-oceannutrient Someofthemostimportantcontributionstoemergefromthe
availabilityandgreatervariabilityinprimaryproductionandexport, ocean time-series programs are reconstructions of biogeochem-
onanannualbasisratesofproductionandparticulatematterexport ical rate processes based on annual mass balances of properties
at HOT and BATS are comparable, with net primary production suchasdissolvedoxygen,dissolvedinorganiccarbon,nitrate,and
averaging (cid:3)14mol C m(cid:2)2yr(cid:2)1 and particulate carbon export nitrogen and carbon isotopes. Among other processes, such
(150m)averaging (cid:3)0.8molCm(cid:2)2yr(cid:2)1,respectively(Table1). approacheshaveprovidedinsightintovariabilityassociatedwith
Upper-ocean primary production (0–100m) at CARIACO is annualratesofnetorganicmatterproduction(ornetcommunity
considerably greater than that observed at either HOT or BATS, production–NCP).AccuratedeterminationsofNCPrequiretime-
withratestypicallyrangingbetween (cid:3)80–145mmolCm(cid:2)2d(cid:2)1 resolved measurements, and hence there are few places in the
butpunctuatedbyperiodsofveryhighproductivity(4200mmol world’soceanswheresuchmeasurementsexist.Overthehistory
Cm(cid:2)2d(cid:2)1)inthelatewinterandearlyspring(Figs.4and5).The ofHOTandBATSavarietyofsamplingandanalyticalapproaches
observed seasonal cycle of primary production at CARIACO have been used to determine NCP, yielding some of the most
reinforces the importance of seasonal-scale changes in trade- comprehensive estimations of NCP anywhere in the world’s
winddrivenupwellingasamajorcontrolonecosystemvariability oceans (Table 2). Such efforts have been strengthened by use of
inthisregion(Muller-Kargeretal.,2004;Thunelletal.,2000).The instrumented remote and autonomous sampling platforms
origin of material sustaining particulate material export at CAR- (moorings,floats,gliders),providinginformationonthecoupling
IACO derives from both autochthonous productivity and terres- betweenhigh-frequencyphysicaldynamicsandvariabilityinnet
trial material introduced through riverine discharge (Lorenzoni organic matter production and export. Together these time-
etal.,2011;Montesetal.,2012;Muller-Kargeretal.,2004).Both resolved sampling approaches have helped transform our view
these processes dominate export at different times of the year, oftemporalvariabilityassociatedwithorganicmatterproduction
with productivity peaking in the late winter and spring during and carbon sequestration in this open-ocean habitat. The
periodsofstrongupwelling,andriverineinputgenerallyincreas- emerging data suggest annual NCP at BATS and HOT may be
ing in the summer (Thunell et al., 2007). As a result, despite similar,ranging2.3–4.7molCm(cid:2)2 yr(cid:2)1 and1.1–4.1molCm(cid:2)2
M.J.Churchetal./Deep-SeaResearchII93(2013)2–15 9
Fig.5. Meanmonthlyprimaryproductionandupper-oceanparticulatecarbonexportatHOT,BATS,andCARIACO.Symbolsrepresentdepth-integrated(0–100m)ratesof
productivityorparticleflux(150mforHOTandBATS,225mforCARIACO);errorbarsarestandarddeviationofthemonthlymeans.NotedifferencesinY-axes.
Table2
RangeofannualestimatesofnetorganicmatterproductionandexportatHOTandBATS.Whereavailableuncertaintiesassociatedwiththedeterminationsareshownin
parentheses.
Timeseries Method Rates Periodof References
site molCm(cid:2)2 measurements
yr(cid:2)1
HOT MixedLayerO2þArbudgets 1.1–3.7(7 1992–2008 Emersonetal.(1997),HammeandEmerson(2006),JuranekandQuay
1.0) (2005),Quayetal.(2010)
DICþDI13Cbudgets 2.7–2.8(7 1988–2002 QuayandStutsman(2003),Keelingetal.(2004),Brixetal.(2004)
1.4)
MooringO2/N2 4.1(71.8) 2005 Emersonetal.(2008)
Sub-mixedlayerfloatprofiles 1.1–1.7 2003–present RiserandJohnson(2008),Johnsonetal.(2010)
(70.2)
Sub-mixedlayerglidersurveys 0.9(70.1) 2005 Nicholsonetal.(2008)
150msedimenttrapsþmigrant 0.9–1.1 1989–2011 HOTcoredata;Emersonetal.(1997),Landryetal.(2001),Hannidesetal.
zooplanktonflux (2009)
BATSand SubmixedlayerO2þAr,Hebudgets 4.3(70.7) 1985–1987 SpitzerandJenkins(1989)
StationS
DICþDI13Cbudgets 2.3(70.9) 1991–1994 Gruberetal.(1998)
3HeandNO3(cid:2)fluxes 2.9–4.5 1985–1987, JenkinsandDoney(2003,1992)
Sub-mixedlayerO2profiles 3.3–4.7 1961–1970 JenkinsandGoldman(1985),JenkinsandWallace(1992)
150msedimenttrapsþmigrant 0.6–2.0 1989–2011 BATScoredata;Lomasetal.(2002),Steinbergetal.(2000,2001,2012))
zooplanktonflux
yr(cid:2)1, respectively (Table 2). Such results are intriguing given (Laws et al., 2000). Such discrepancies provide sobering remin-
differences in the timing and magnitude of vertical delivery of ders that there remain a number of unresolved issues central to
nutrients to the upper ocean observed at these sites (Fig. 3). ourunderstandingofoceanecosystemfunctioning.
Moreover,thesegeochemicalmassbalancesappearasmuchas4- Among the most recognized biogeochemical measurements
fold greater than predicted based on sediment trap estimates of conducted by these programs are those documenting time varia-
carbon export (Table 2), and estimates derived from ocean bilityassociatedwithseawaterCO (Fig.6).Thesemeasurementsat
2
circulation (Schlitzer, 2004) and satellite ocean-color models HOT, BATS, and CARIACO, together with measurements conducted
10 M.J.Churchetal./Deep-SeaResearchII93(2013)2–15
Fig.6. Meanannualnear-surfaceoceanpCO2(redcircles)andseawaterpH(bluediamonds)atHOT,BATS,andCARIACO.Errorbarsdepictstandarddeviationsofannual
means.(Forinterpretationofthereferencestocolorinthisfigurecaption,thereaderisreferredtothewebversionofthisarticle.)
as part of the ESTOC and MBARI time-series programs, comprise high-qualitymeasurementsoverlongperiodsoftimeisthefounda-
some of the most robust decadal-scale datasets available for tion of success for these programs, and retaining well-trained
describing the response of the ocean to progressive increases in scientists and technical staff are essential to these efforts. While
atmospheric CO . These measurements indicate that over annual certifiedreferencematerialsprovideameanstotracethequalityof
2
time scales, HOT and BATS are both weak to moderate sinks for an oceanographic measurement, for many of the biogeochemical
atmospheric CO (Bates et al., 1996; Winn et al., 1998), while measurements (particularly most rate measurements), no certified
2
CARIACO is a net source of CO to the atmosphere (Astor et al., standards exist. Furthermore, developing confidence that measure-
2
2005,2013).Time-seriesmeasurementsatHOT,BATS,andCARIACO mentsconductedatdifferentsitesareintercomparabledemandsthat
documentprogressiveincreasesinthepartialpressureofCO (pCO ) theseprogramscontinuetoregularlyparticipateincommunity-wide
2 2
in the near-surface ocean with concomitant decreases in seawater effortsdirectedtowardstandardizingmethodologiesandanalyses.
pH(Fig.6).Thelong-termincreaseinseawaterpCO atHOT,BATS A significant scientificchallengehas beento design sampling
2
andCARIACOappearsimilartotherateofCO accumulationinthe schemesappropriatetocapturingimportantmodesofecosystem
2
atmosphere ((cid:3)1.7matm yr(cid:2)1), with concomitant long-term variability. Despite near-monthly sampling schedules these pro-
decreasesinseawaterpHranging(cid:2)0.0017to(cid:2)0.0019y(cid:2)1.Despite grams spendo20% of the year on site observing ecosystem
similarlong-termtrends,thereissubstantialinterannualtoseasonal dynamics, implying that some important processes will be
scale variability in upper ocean CO attributable to local- and under-sampled in both space and time (Wiggert et al., 1994).
2
regional-scale ecosystemdynamics(Astor et al., 2013; Bates etal., Episodic events and processes that exert high frequency varia-
1996; Dore et al., 2003; Gruber et al., 1998, 2002; Keeling et al., bility can be missed with this sampling strategy (Levin, 1992;
2004). Interannual variations in pCO and pH at all three sites Munk,2000).Moreover,limitedsamplinginthespatialdomainis
2
depends on regional to basin scale fluctuations in ocean-climate also an issue that can lead to aliasing of Eulerian processes
connectivityandbiologicalactivity,withvariationsintemperature, attributable to horizontal advection, thereby hindering differen-
evaporation–precipitation, and upper ocean mixing all imparting tiating time-dependent local changes from those attributable to
characteristic signatures onCO system dynamics in these regions spatialvariabilityontheregionalscale.
2
(Astoretal.,2005;Bates,2007;Doreetal.,2003,2009).
4.2. Transformativetechnologies
4. Chartingthefuturecourse The science of observing the ocean has made huge advances
since the 1980s. While the disciplinary expansion of oceanogra-
4.1. Wherethefuturemeetsthepast phy in the 20th century was largely propelled by ship-based
expeditionaryscience,thenewgenerationofoceanobservations
Ocean time-series programs provide critical long-term records capitalizesontechnologicaladvancesinremoteandautonomous
needed for assessing the interactions between chemistry, biology, sensingplatforms.FollowingtheendofWorldWarII,duringthe
physicsandgeology.Thescientificvalueoftheseprogramscontinues eraoftenreferredtoas‘‘goldenageofoceanography’’,shipboard
toincreasethroughsustainedobservations.However,theexpansion researchstoodastheprimarymeansofgatheringinformationon
ofoceantime-seriesresearch,bothindurationofindividualprograms the ocean. However, the ‘‘golden age’’ of oceanography rapidly
and the number of programs, during the 1990s taught important yielded to the ‘‘era of the electron’’ where improved platform
lessons,somerelatedtoscience,othersontherealitiesandlogisticsof engineering, data storage, sensor stability and durability, and
sustaining long-term science programs (Karl, 2010). Time-series communications technologies have thrown the door wide open
programs are resource intensive and thus maintaining ocean com- tonewtechnologiesforsensingthesea.Anewinternationalwave
munity support for these programs requires strong and positive of contemporary ocean observatories rely on measurements
leadershipandadedicatedteamofpeoplethatunderstandthevalue conducted from instrumented remote sensing platforms includ-
of long-term observations. The requirement to maintain consistent, ing satellites, moorings, floats, and various autonomous vehicles
M.J.Churchetal./Deep-SeaResearchII93(2013)2–15 11
(e.g. http://www.eurosites.info/index.php; http://www.oceanob ideal for developing, testing, and implementing novel ocean-
servatories.org/). Advances in sensor technologies now provide observing technologies. Moreover, such projects demonstrated
small, low-power, stable instrumentation that can be outfitted that enhancing the observational capacities of the time-series
onto diverse ocean platforms (Johnson et al., 2009; Perry and programs does not necessarily require expansion of the existing
Rudnick, 2003). Such technological advances therefore have shipboard programs. Rather, the shipboard programs and their
provided new opportunities to enhance observational capacity long-termdatarecordsserveastheunifyingcorestructurefrom
aroundshipboardprograms. which new science directions and observational technologies
There are numerous examples of studies that have leveraged arebuilt.
ship-based time-series programs with higher frequency, spatio- Overthenextdecade,theshipboardprogramsmustcontinue
temporally resolving, autonomous and remote measurements to be proactive about promoting the implementation of new
(Conte et al., 2003; Emerson et al., 2002, 2008; Johnson et al., ocean sensing technologies at these sites. However, despite the
2010; Letelier et al., 2000; McGillicuddy et al., 1998; Muller- growinglistofpotentialapplicationsforremoteandautonomous
Karger et al., 2004; Nicholson et al., 2008). Such studies yield sensingofoceandynamics,thereremainseverallargehurdlesto
further insightinto scalesof variability associated with plankton be overcome before ship-based time-series become obsolete.
metabolism and biomass, carbon export, nutrient fluxes, water- Currently no combination of autonomous or remote sensing
massventilation,andair–seagas exchanges,toname a few. Ina technologies could be employed to replace the full suite of
recentexample,withsupportfromNSFandtheNationalOceano- high-qualitymeasurementsroutinelyconductedaspartofinter-
graphicPartnershipProgram,SteveRiser(UniversityofWashing- disciplinary shipboard time-series programs. In many cases the
ton) and Ken Johnson (MBARI) instrumented quasi-Lagrangian, long-termaccuracyofsuchsensorsremainsunknown,challenged
vertically profiling floats with nitrate, oxygen, fluorescence, and in part by non-trivial issues associated with biofouling and
backscatter sensors (http://www.mbari.org/chemsensor/floatviz. instrumentstability(Dickey,1991;Johnsonetal.,2009).Perhaps
htm). Several of these floats have now been deployed at HOT, most importantly, there are currently a limited set of sensors
BATS,andStationP,providingnewtoolsforexaminingsimilarities readily available for detecting many of the key biological and
anddifferencesinecosystemprocessessuchasnutrientsupplyto chemicalpoolsandfluxesknowntobeclimatesensitiveandplay
theeuphoticzone(andhighlightingpotentiallyunderappreciated roles in the ocean carbon cycle. While numerous ‘‘in water’’
mechanismssuchphytoplanktonverticalmigration),netcommu- sensors are currently available and widely used for detecting
nityproduction,andlengthscalesoforganicmatterremineraliza- ocean hydrographic variability, sensors for autonomous and
tion(Martzetal.,2008;RiserandJohnson,2008).Inaddition,with remote detection of ocean biogeochemistry, beyond nutrient
support from the Gordon and Betty Moore Foundation and NSF, and oxygen dynamics, have proven more difficult to develop
ocean gliders have been in service at or around Station ALOHA andimplement.Forexample,todate,therearefewtoolsavailable
since 2008, providing insight into spatiotemporal variability in for remote quantification of plankton community structure
temperature, salinity, oxygen, backscatter, and fluorescence (although see Scholin et al., 2009). Moreover, although sensors
(http://hahana.soest.hawaii.edu/seagliders/index.php). These pro- foropticalbaseddeterminationsofnitrateareavailable(Johnson
grams highlight a few examples where remote or autonomous andColetti,2002),sensorsfordetectionofphosphate,silicate,and
sensing approaches leveraged the shipboard programs to test dissolvedorganicorinorganiccarbonarenotyetwidelyavailable.
hypothesesgeneratedfromthehistoricaltime-seriesdata. Thereare stillfewerinstrumentsthat canmakedirectmeasure-
Hydrographic and biogeochemical moorings have been ments of ecosystem rate processes, versus the time-derivative
deployed for substantial periods of time at each of the OCB geochemical estimates of rate processes (e.g., Nn and related
stations.TheBermudaTestbedMooring(BTM)operatedformore variables). Such measurements are fundamental to informing
than a decade (1994–2007) near the BATS site, forging new, our understanding of plankton ecology and ultimately biogeo-
collaborative science partnerships that informed understanding chemicalcontrolsoncarbonsequestrationinthevastoceangyres.
of episodic physical forcing on ocean biogeochemistry (Bates
etal.,1998;Dickeyetal.,1998;McNeiletal.,1999).Since1997, 4.3. Improvedprocess-levelunderstandingandlinkagesto
varioushydrographic,biogeochemical,andmeteorologicalmoor- ecosystemmodels
ings have been maintained at or near Station ALOHA, including
HALE ALOHA (1997–2000), MOSEAN (2004–2007), and WHOTS The existing ocean time-series records clearly demonstrate
(2004–present). These moorings have provided critical observa- biogeochemical and hydrographic variability in ecosystem
tions for understanding high-frequency variability in ecosystem dynamicsoccurringoveralargerangeoftimescales.Concentra-
processes (Church et al., 2009; Emerson et al., 2002; Karl et al., tionsofchlorophyll,ratesofprimaryproduction,nutrientinven-
2003). Recently, scientists and engineers from the University of tories and stochiometries, export of organic material from the
Hawaii led the successful installation of the ALOHA Cabled upper ocean, and stocks of organisms and plankton community
Observatory (http://aco-ssds.soest.hawaii.edu/ACO/index.php). structure have all been shown to vary over seasonal to sub-
By takingadvantage of anexisting seafloor fiber optic cable, the decadal time scales. However, in many of these examples, the
ACO provides a seabed node for powering instruments and mechanisms underlying the observed time-varying changes
transmitting data. Such infrastructure has the promise to trans- remain obscure. Long-term increases (HOT, BATS) or decreases
form thesea sensing capabilities at StationALOHA. At CARIACO, (CARIACO) of primary production and inventories of chlorophyll
subsurface hydrographic and current moorings have been reportedatthesesiteshavebeenattributedtobasin-scaleclimate
deployed sporadically over periods spanning several years fluctuations (Chavez et al., 2011; Corno et al., 2007; Saba et al.,
(Alvera-Azca´rate et al., 2008), and moored sediment traps have 2010; Taylor et al., 2012); however, our understanding of the
beensamplingroutinelysince1996(Benitez-Nelsonetal.,2007; processes linking ocean–climate to changes in seawater biogeo-
McConnelletal.,2009;Tedescoetal.,2007;Thunelletal.,2007). chemistry remains rudimentary. Alteration in phytoplankton
These previous and ongoing efforts to enhance the observa- productivityandbiomass atthesesites couldstem frombottom
tionalcapacitiesatthetime-seriessiteshaveallreliedheavilyon up processes such as changes in light (as a consequence of
the scientific and logistical infrastructure afforded by the ship- changes in upper ocean stratification) or changes in nutrient
board programs. The many years of developing highly skilled supply (Bidigare et al., 2009). Alternatively, temporal variations
workforcesandcapableinfrastructuremakethetime-seriessites in various top-down processes could control plankton biomass