Deep Sea Coral Evidence for the state of the Southern Ocean Biological Pump (and Circulation) During the Last Glacial Period and Deglaciation

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Joshua Williams
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Andrews Laura Robinson, Bristol Our Target Archive for Past Climate Reconstruction Tony Wang, Princeton

1 Deep Sea Coral Evidence for the state of the Southern Ocean Biological Pump (and Circulation) During the Last Glacial Period and Deglaciation Sophie Hines, Caltech Andrea Burke, St. Andrews Laura Robinson, Bristol Our Target Archive for Past Climate Reconstruction Tony Wang, Princeton (Caltech) Danny Sigman, Princeton James Rae, St. Andrews Eleni Anagnostou, ETH Rob Sherrell, Rutgers D. dianthus, ~5cm tall, ~1mm/yr extension rate

2 1 Sv 5 Sv A 7 Box Model to study Some Stuff 5 Sv Sv 5. 1 Sv 1 Sv 2 Sv Each Box has: PO4 DIC Alk Δ 14 C Green arrows are productivity raining into the interior, other arrows are circulation (Sv). The productivity rule is P = k[po4].

3 Atm pco2 in a Harvardton Bears Experiment 35 Atm pco High Lat South Nutrient Utilization Efficiency SOMix Value (Sv) SOMix Value (Sv) HighLat South Productivity Const (1/sec) x HighLat South Productivity Const (1/sec) x 1 9 -Atm CO2 follows nutrient utilization efficiency until low values of SO Mix (f17)

4 The importance of preformed PO Atm pco2 (ppmv) Deep South [CO3] Atm pco2 (ppmv) Deep South [CO3] Deep South [CO3] Atm pco2 (ppmv) Deep South [CO3] Deep South [CO3] Total Deep Preformed [PO4] x Total Deep Preformed [PO4] x Total Deep Preformed [PO4] x Atm pco2 (ppmv) Total 5 Deep Preformed [PO4] x Total Deep Preformed x [PO4] 1 15 Harvardton Bears with isolated deep cell bio pump not dependent on [PO4] Total D This is for the soft tissue pump only, but it is probably the biggest term for G/I pco2

5 A Kohfled Plot (or a summary of many studies of LGM productivity) Polar waters show lower export production, sub-polar waters show higher production Kohfeld et al., 213

What about the circulation component? Western Atlantic GEOSECS D13C (PDB) 1.2.8.8. 8-2.8 Depth (m) -1-3.4-4 -5.

6 What about the circulation component? Western Atlantic GEOSECS D13C (PDB) Depth (m) δ13c -6 Western Atlantic Glacial D13C (PDB) 1.6 Depth (m) Cd/Ca Latitude Curry and Oppo, 25 Lynch-Stieglitz et al., 25

7 The depth structure of a conservative tracer in the Atlantic at the LGM Brazil Margin (3 S) Blake Ridge (3 N) δ 18 Obenthic δ 18 OLGM-δ 18 OHolocene Curry and Oppo, 25 Keigwin, 24 ΨΔC = KzCz(area) Ψ/Kz is about 8x larger at the LGM LAF, 213

8 Glacial Maximum T and S for the Deep Ocean (Based on pore fluid measurements of [Cl] and δ 18 O) Modern North Atlantic Last Glacial Max Hydrography Theta ( C) 1. 5 Modern South Pacifi c Modern Southern Ocean Site m Eq. Pacific Site m Southern O Site m N. Atlantic Site m S. Pacific B. Site m N. Atlantic Salinity (psu ) Adkins, McIntyre, and Schrag, 22

9 LGM Benthic δ 18 O and δ 13 C Show 2-Cell Separation Adkins, 213, but after: Duplessey et al., 22

10 1 warm/salty The LGM really does seem to be a 2-cell structure (at least in 3 cold/fresh.7 the Atlantic) 4 5 sea ice Interglacial Modern Atlantic fresh water? 1 cold/fresh However, the effects of salt and heat don t oppose each other cold/salty S Eq 4 N Glacial Atlantic Glacial

11 The Opposing Contributions of T and S to Density Lead to some Cool Features of the Modern Ocean Potential Temperature θ [degc] 3 Salinity[PSS-78] DEPTH [M] S 2 S EQ 2 N 4 N 6 N Ocean Data View A. B. DEPTH [M] 4 S 2 S EQ 2 N 4 N 6 N Ocean Data View DEPTH [M] Potential Density Anomaly σ [kg/m 3 ] 4 S 2 S EQ 2 N 4 N 6 N C. D. Ocean Data View AABW = -.89 C S = psu = = = Push down to 3, meters = End Member Potential Density NADW = 2.1 C S = psu = = Adkins, 213

12 Samples of Fossil Deep-Sea Corals Adkins cruises S. of Tasmania Robinson cruises in Drake Passage

13 Populations move in space and time 25 Margolin et al., 214 Thiagarajan et al., 214

14 We have two radioactive clocks in the same sample; 238 U U - 23 Th and Radiocarbon. This lets us solve the first order decay equation: N=N e -λ t for the initial amount of 14 C in the ocean where the coral grew. Similar calculation for Benthic- Planktonic Forams

15 Δ 14 C of the Intermediate and Deep Ocean through time 14 C ( ) Drake Passage, AAIW Tasmania, deep AAIW Drake Passage, UCDW Chatham Rise, 2314 m South Atlantic, 377 m South Atlantic, 4981 m IntCal13 corals forams Calendar Age (kyr.bp) dc atm dt = Pr oduction λc atm Ocean Exchange

16 Radiocarbon has a mid-depth bulge at LGM Drake Passage and Deep South Atlantic 1 Depth (m) (Burke & Robinson, 212) (Skinner et al., 21) (Barker et al., 21) Atmosphere normalized 14 C ( ) Burke, Stewart, et al., 215

17 Corals record δ 15 N of raining organic matter Wang et al., 214

18 The LGM was higher in δ 15 N in the Polar and Sub-polar Antarctic zones Both regions draw down [NO3] to very low levels and lateral exchange between the zones was greatly reduced Wang et al., 217

19 A complimentary view of in situ phosphate S. of Tasmania [PO4] (umol/kg) Ka 16.7 Ka Ka Ka Ka 1 Ka modern modern corals Depth (m) Anagnostou et al., unpublished

20 Boron Isotopes allow for an estimate of paleo ph (which we now know is also pco2)

21 The lower cell degasses CO2 along with the whole atmosphere rise since the LGM Drake Passage SAZ (upper cell) Drake Passage Antarctic Zone (lower cell) The ph of the lower cell rises as it loses CO2 to the atm. Rae et al., unpublished

22 A focus on the deglaciation shows the upper cell is a compliment to the lower cell pco2 history Drake Passage SAZ (upper cell) ph drops abruptly at end of H1 when 2 cells merge for 1st time. Rae et al., unpublished

23 Some Concluding Thoughts 1. The LGM was separated into 2 distinct deep circulation cells. 2. The ventilation rate of the southern cell seems to have increased during the LGM, but not during the whole glacial period. 3. Deep-sea coral populations off of Tasmania feel the rapid climate changes seen in ice cores. 4. Nutrient utilization in both the Polar and Sub-Antarctic Zones increased at the LGM. 5. Phosphate concentrations (preformed?) dropped by ~2x at the LGM off of Tasmania in Intermediate waters. 6. The ph of the deep cell over the deglaciation reflects the degassing of respired CO2 back to the atmosphere, while the upper cell show centennial variability perhaps related to circulation changes.

Geoffrey (Jake) Gebbie Research Associate, Harvard University Visiting Scientist, MIT

Our basic understanding of past ocean circulation Geoffrey (Jake) Gebbie Research Associate, Harvard University Visiting Scientist, MIT ACDC Summer School, 5 June 2009 The view down a borehole (Helen Freeman,