South Atlantic intermediate water mass geometry for the last glacial maximum from foraminiferal Cd/Ca

Makou, Matthew; Oppo, Delia W; Curry, William B

doi:10.1029/2010pa001962

Cited by 33 publications

(32 citation statements)

References 41 publications

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“…The western Atlantic glacial δ 13 C section includes published benthic data compiled previously (Curry & Oppo, ), data published since then (Burckel et al, ; Freeman et al, ; Hodell et al, , ; Hoffman & Lund, ; Keigwin & Swift, ; Lund et al, ; Lynch‐Stieglitz et al, ; Oppo et al, ; Poggemann et al, ; Praetorius et al, ; Rickaby & Elderfield, ; Tessin & Lund, ; Thornalley et al, ; Voigt et al, ), and our new data from the eight cores on the Demerara Rise, ranging in water depth from 376 to 2,642 m (Table and supporting information tables). The Western Atlantic CdW section includes data compiled previously (Marchitto & Broecker, ), data published since then (Makou et al, ; Poggemann et al, ), and new data from the Demerara Rise and Blake Outer Ridge. Revised distribution coefficients, discussed below, were applied to all published and new Cd/Ca data (supporting information tables).…”

Section: Methodsmentioning

confidence: 99%

Data Constraints on Glacial Atlantic Water Mass Geometry and Properties

Oppo

Gebbie

Huang

et al. 2018

Paleoceanog and Paleoclimatol

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The chemical composition of benthic foraminifera from marine sediment cores provides information on how glacial subsurface water properties differed from modern, but separating the influence of changes in the origin and end‐member properties of subsurface water from changes in flows and mixing is challenging. Spatial gaps in coverage of glacial data add to the uncertainty. Here we present new data from cores collected from the Demerara Rise in the western tropical North Atlantic, including cores from the modern tropical phosphate maximum at Antarctic Intermediate Water (AAIW) depths. The results suggest lower phosphate concentration and higher carbonate saturation state within the phosphate maximum than modern despite similar carbon isotope values, consistent with less accumulation of respired nutrients and carbon, and reduced air‐sea gas exchange in source waters to the region. An inversion of new and published glacial data confirms these inferences and further suggests that lower preformed nutrients in AAIW, and partial replacement of this still relatively high‐nutrient AAIW with nutrient‐depleted, carbonate‐rich waters sourced from the region of the modern‐day northern subtropics, also contributed to the observed changes. The results suggest that glacial preformed and remineralized phosphate were lower throughout the upper Atlantic, but deep phosphate concentration was higher. The inversion, which relies on the fidelity of the paleoceanographic data, suggests that the partial replacement of North Atlantic sourced deep water by Southern Ocean Water was largely responsible for the apparent deep North Atlantic phosphate increase, rather than greater remineralization.

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Section: Methodsmentioning

confidence: 99%

Data Constraints on Glacial Atlantic Water Mass Geometry and Properties

Oppo

Gebbie

Huang

et al. 2018

Paleoceanog and Paleoclimatol

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“…Additional observations include 3 δ 13 C c observations from the Demerara Rise (D.W. Oppo and W.B. Curry, personal communication, 2014), 15 paired δ 13 C c and Cd/Ca measurements [ Makou et al , ], and all reported δ 13 C c values from Marchitto and Broecker [] that were not present in other compilations. In total, the model is constrained with 241 δ 13 C c , 87 Cd/Ca, and 174 δ 18 O c observations (Figure ).…”

Section: Lgm Water Mass Decompositionmentioning

confidence: 99%

“…The modeled LGM 13 C as values do not give such a clear picture. AABW has a 13 C as value lower than −0.5‰, but AAIW is slightly positive in accord with previous works [Oppo and Horowitz, 2000;Makou et al, 2010]. GNAW is reconstructed to have 13 C as of 0‰-0.2‰, which is a less distinct signal than the 0.5‰ inferred by Marchitto and Broecker [2006].…”

Section: Air-sea Signature Of 13 Cmentioning

confidence: 99%

How much did Glacial North Atlantic Water shoal?

2014

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Observations of 13 C and Cd/Ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the Last Glacial Maximum, with the degree of shoaling being significant enough for the water mass to be renamed Glacial North Atlantic Intermediate Water. These nutrient tracers, however, may not solely reflect changes in water mass distributions. To quantify the distribution of Glacial North Atlantic Water, we perform a glacial water mass decomposition where the sparsity of data, geometrical constraints, and nonconservative tracer effects are taken into account, and the extrapolation for the unknown water mass end-members is guided by the modern-day circulation. Under the assumption that the glacial sources of remineralized material are similar to that of the modern day, we find a steady solution consistent with 241 13 C, 87 Cd/Ca, and 174 18 O observations and their respective uncertainties. The water mass decomposition indicates that the core of Glacial North Atlantic Water shoals and southern source water extends in greater quantities into the abyssal North Atlantic, as previously inferred. The depth of the deep northern-southern water mass interface and the volume of North Atlantic Water, however, are not grossly different from that of the modern day. Under this scenario, the vertical structure of glacial 13 C and Cd/Ca is primarily due to the greater accumulation of nutrients in lower North Atlantic Water, which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial Atlantic.

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“…We might expect that sea ice expansion in the Southern Ocean could influence the production of mode and intermediate waters by altering surface budgets of heat and freshwater [Naveira Garabato et al, 2009] and modifying their preformed characteristics [Makou et al, 2010]. Changes in northward advection of intermediate waters in turn could impact silicic acid leakage.…”

Section: 1002/2013pa002588mentioning

confidence: 99%

Different mechanisms of silicic acid leakage and their biogeochemical consequences

2014

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In the modern ocean, silicic acid is effectively trapped in the Southern Ocean. According to the silicic acid leakage hypothesis, a loosening of this trapping may have contributed to low atmospheric CO 2 during glacial times. Using a model with dynamical feedbacks in ocean physics and biology, we explore three distinct mechanisms to loosen the trapping and trigger silicic acid leakage from the Southern Ocean: sea ice expansion, weaker winds, and iron addition. The basic idea of the iron addition mechanism was previously explored using a simple box model. Here we confirm the main results of the earlier work and demonstrate further that sea ice expansion and weaker southern westerlies can also trigger silicic acid leakage. The three mechanisms are not mutually exclusive, and their biogeochemical consequences are dissimilar in terms of the spatial patterns of Si:N uptake and the relative changes in opal and particulate organic carbon fluxes both in and outside the Southern Ocean. While it is not entirely clear how sea ice, winds, and iron deposition were different during the last glacial period compared to today, we examine the synergistic effects of these three triggers in one simulation. In this simulation, the combination of sea ice and iron reproduces the north-south dipole of productivity recorded in export production proxies, but effects of the iron perturbation seem to dominate the overall biogeochemical response.

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South Atlantic intermediate water mass geometry for the last glacial maximum from foraminiferal Cd/Ca

Cited by 33 publications

References 41 publications

Data Constraints on Glacial Atlantic Water Mass Geometry and Properties

Data Constraints on Glacial Atlantic Water Mass Geometry and Properties

How much did Glacial North Atlantic Water shoal?

Different mechanisms of silicic acid leakage and their biogeochemical consequences

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