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BESA(ME): Biogeochemistry and Ecology of the Sub‐Antarctic (and Mode water
Export)
William “Barney” BalchBigelow Laboratory for Ocean Sciences
E. Boothbay, ME 04544 USA201
8 OCB
Worksh
op
Roadmap‐ A few vignettes• Brief review of physics of the Southern Oceansystem and Subantarctic Mode Water
• The Great Calcite Belt and SAMW associations• Chemical and biological conditioning of SAMWby coccolithophores and diatoms
• Eddy influences in the Subantarctic• View of the Great Calcite Belt from the Atlanticbasin and a conceptual model
• Summary
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Southern Ocean‐ Deacon defined the physics of the global system of ocean circulation…
Sir George DeaconPolarFront
SubAntFront
AgulhasRetCurrent
Deacon, G. E. R. (1933), A general account of the hydrology of the South Atlantic Ocean, Discovery Rep., 7, 171‐238.
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Sub‐Antarctic Mode Water:• is a homogeneous layer with uniform density; sitsover lower salinity AAIW
• formation is associated with deep mixed layers, wellventilated with 95% oxygen saturation; 17‐18 Svproduced in all three ocean basins
• density =26.5 to 27.1• silicate is depleted relative to nitrate (residualnitrate)
• exchange FW and heat between the Southern Oceanand Subtropical gyres
• supply nutrients to adjacent Subtropical gyres• shows circulation time scales of decades
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Fate of SAMW• Estimated to control 75%
of the biologicalproduction of watersnorth of 30oS
• Controls functionalgroups of these waters,depending on the amountof silicate that “leaks”from the Southern Ocean
• Subducted SAMW arrivesto the equatorial zone~40 years later.
Sarmiento et al., 2004; Nature
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Balch, Bigelow Laboratory for Ocean Sciences
a
Visible PIC color fronts: PF; SAF; STF
This image cannot currently be displayed.
Stn 27; 20m
Stn 119; 7m
CruiseSEMs showing coccolithophores
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2016
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Great Calcite Belt sits in high‐velocity circumpolar currents of the Southern
Ocean…likely sites of high Ekman pumping
Balch et al., 2016; GBC
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Plot surface PIC concentration in temperature/salinity space
20
18
22
24
25 26
27
28
29
30
31
Isopleths of density; sigma theta PIC (mol m‐3)
0.01
0.003
0.001
0.0003
0.0001
0.00003
30 31 32 33 34 35 36 37 38 39 Salinity
30
25
20
15
10
5
0
Tempe
rature (oC)
PIC (Dec’12)
21
19
23
SAMW; 26.5‐27.1Cerovečki et al., 2013
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Coccolithophore calcification lowers the alkalinity and increases the pCO2
Nick Bates, BIOS Balch et al., 2016; GBC
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‐Big diatoms, well silicified;‐Picos, nanos, coccos and dinosoutcompeted‐Low calcificationNet CO2 drawdown (NCOP>NCC)‐High Export flux‐Low transfer efficiency
‐Coccos & small diatoms dominate (e.g. small Fragillariopsis)‐Picos, nanos, dinos coexist and covary‐No impact on pCO2 (NCOP = NCC)‐Moderate Export flux‐Low‐moderate transfer efficiency
‐Coccos outcompete diatoms,picos, nanos, and dinos
‐High calcificationNet CO2 source (NCC>NCOP)‐Moderate Export flux‐High transfer efficiency
‐Coccos , dinos, nanos and picos coexist and covary‐Low to moderate calcification‐Neutral to slight pCO2 source (NCC=>NCOP) Moderate Export flux
Mandala for biogeochemistry and ecology in the GCBIro
n concen
tration
Balch et al., 2016; GBC
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Eddies and Sub‐Antarctic Mode Water
Koch‐Larrouy et al. 2010, Ocean Dynamics
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PIC‐rich eddies
• Eddies spinningoff of SAF
• PIC rich eddiessurvive formonths
• Seen previouslyRead JF etal.(2007) DSR II
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Altimetry day shows importance of eddy mixing…
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Community Earth System model (CESM)• Global eddy‐resolving
integration of CESM Upper100m integrals
• Includes ocean BGCcomponent called theBiogeochemical ElementalCycle (BEC) mode
• Represents multiple nutrientco‐limitation (N, P, Si, and Fe)
• 3 explicit phytoplanktonfunctional groups (diatoms,diazotrophs, and “small”pico/nano phytoplankton),and one implicit group(calcifiers)
Long, NCAR
NO3 (mol m‐2)
2.8
2.0
1.2
0.40
10
7.5
5
2.5
0
Si(OH)4 (mol m‐2)
PIC prod.(mol m‐2)
166.32.510.390.250.0630.0250.01
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Low [coccolithophores] in the Equatorial Atlantic…why?
Balch et al., GBC. in review
SAMW
10 AMT Cruises
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Conceptual View of Subantarctic mode water export… “So what?”
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Summary: BESA(ME)Biogeochemistry and Ecology of the Sub‐
Antarctic (and Mode water Export)• The biogeochemistry and ecology of the Subantarctic (asdescribed in the mandala) likely influence the BGC andecology of the subtropics and tropics
• The linkages are physical (via SAMW)• Minerogenic phytoplankton (diatoms and calcifiers)condition SAMW prior to its subduction, which could affectgrowth of ballast‐producers and export of waters well to thenorth
• BESA(ME) cruises in January 2019, 2020 in Indian Sector ofthe Southern Ocean (Balch [BLOS], McGillicuddy [WHOI],Long[NCAR], Morton[SFU], Bates[BIOS], Brownlee[MBA,UK])
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Thank you!ACKNOWLEDGEMENTS:• Bruce Bowler, Dave Drapeau, Laura Lubelczyk & Sarah Rauschenberg
(Bigelow Laboratory for Ocean Sciences), Annie Warner & Brittney Honisch(Colby College); Rebecca Garley, Dafydd Evans, Kristen Shake & AndrewCollins (BIOS); Steven Pike, Dan Ohnemus, Sarah Rosengard & MaureenWisch (WHOI), Rebecca Fowler (Columbia Univ.), Marina Van der Eb (U.Maine Orono), Michael Brown (Rutgers), Patrick Holligan, Jason Hopkins &Helen Smith (NOC), Cecilia Balestreri (MBA, Plymouth, UK), Angel Ruacho,Matt Durham & Daniel Young, Melissa Miller, John Calderwood, BrentDevries (SIO); Norman Kuring‐ NASA Goddard
• Captains and crew of: R/V Melville and R/V Revelle• Goddard Ocean Color Group; Ocean Data View• NASA and NSF support
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