Late-Quaternary changes in productivity of the Southern Ocean

Anderson, Robert F.; Kumar, Niraj; Mortlock, Richard A.; Froelich, Philip N.; Kubik, Peter W.; Dittrich-Hannen, B.; Suter, M.

doi:10.1016/s0924-7963(98)00060-8

Cited by 90 publications

(81 citation statements)

References 46 publications

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“…There are, however, two peaks in authigenic uranium at 30 and 140 ka. Authigenic U is formed in sediments which are experiencing reducing conditions due to a depletion of O 2 in the overlying water or to a high flux of organic carbon from the overlying water column [Anderson et al, 1998;Kumar et al, 1995;Mangini et al, 2001]. Peaks in U auth observed in WIND 28K may have initially extended to younger sediment, but been subsequently removed when oxic conditions returned and ''burnt down'' into existing sediment [Mangini et al, 2001].…”

Section: Authigenic Umentioning

confidence: 99%

“…Studies in the Atlantic [Gherardi et al, 2005;McManus et al, 2004;Yu et al, 1996] have shown it to be a useful proxy for circulation, and in the Southern Ocean for productivity [Anderson et al, 1998;Kumar et al, 1995] and/or particle type [Chase et al, 2002]. In this study, the temporal and spatial data coverage of ( 231 Pa xs / 230 Th xs ) 0 in the Indian Ocean is extended, and the ratio used to provide a record of the rate of past deep water flow into the Indian Ocean from the Southern Ocean.…”

Section: Introductionmentioning

confidence: 99%

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Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios

2007

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A down‐core 231Pa/230Th record has been measured from the southwestern Indian Ocean to reconstruct the history of deep water flow into this basin over the last glacial‐interglacial cycle. The (231Paxs/230Thxs)0 ratio throughout the record is nearly constant at approximately 0.055, significantly lower than the production ratio of 0.093, indicating that the proxy is sensitive to changes in circulation and/or sediment flux at this site. The consistent value suggests that there has been no change in the inflow of Antarctic Bottom Water to the Indian Ocean during the last 140 ka, in contrast to the changes in deep circulation thought to occur in other ocean basins. The stability of the (231Paxs/230Thxs)0 value in the record contrasts with an existing sortable silt () record from the same core. The observed variability is attributed to a local geostrophic effect amplifying small changes in circulation. A record of authigenic U from the same core suggests that there was reduced oxygen in bottom waters at the core locality during glacial periods. The consistency of the (231Paxs/230Thxs)0 record implies that this could not have arisen by local changes in productivity, thus suggesting a far‐field control: either globally reduced bottom water oxygenation or increased productivity south of the Opal Belt during glacials.

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Section: Authigenic Umentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios

2007

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“…Calvert and Pedersen, 1993;François et al, 1993François et al, , 1997Dean et al, 1994Dean et al, , 1997Rosenthal et al, 1995;Crusius et al, 1996Crusius et al, , 2000Anderson et al, 1998;Adelson et al, 2001;Nameroff et al, 2004). Other complications on the use of RSMs involve the present understanding of their respective global mass balances.…”

Section: Introductionmentioning

confidence: 99%

Insights on geochemical cycling of U, Re and Mo from seasonal sampling in Boston Harbor, Massachusetts, USA

Morford

Martin

Kalnejais

et al. 2007

Geochimica et Cosmochimica Acta

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3Benthic chamber experiments including the nonreactive solute tracer, Br -, indicated that sediment irrigation was very important to solute exchange at the study site.The enhancement of sediment-seawater exchange due to irrigation was determined for the nonreactive tracer (Br -), TCO 2 , NH 4 + , U and Mo. The comparisons between these solutes showed that reactions within and around the burrows were very important for modulating the Mo flux, but less important for U. The effect of these reactions on Mo exchange was highly variable, enhancing Mo (and, to a lesser extent, U) uptake at times of relatively modest irrigation, but inhibiting exchange when irrigation rates were faster.These results reinforce the observation that Mo can be released to and removed from pore waters via sedimentary reactions.The removal rate of U and Mo from seawater by sedimentary reactions was found to agree with the rate of accumulation of authigenic U and Mo in the solid phase. The fluxes of U and Mo determined by in situ benthic flux chamber measurements were the largest that have been measured to date. These results confirm that removal of redoxsensitive metals from continental margin sediments underlying oxic bottom water is important, and suggest that continental margin sediments play a key role in the marine budgets of these metals.4

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“…Records of biogenic opal content in deep-sea sediments from the Atlantic sectors of the Southern Ocean reveal a pronounced meridional asymmetry Mortlock et al, 1991;Kumar et al, 1995;Anderson et al, 1998), with glacial-interglacial changes in composition of sites lying approximately either side of the position of the presentday Antarctic Polar Front (APF) being opposite in sign (e.g., see Fig. 3).…”

Section: Testing Hypotheses For G-i Change Using Synthetic Sediment Cmentioning

confidence: 99%

Application of sediment core modelling to interpreting the glacial-interglacial record of Southern Ocean silica cycling

Ridgwell

2007

Clim. Past

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Abstract. Sediments from the Southern Ocean reveal a meridional divide in biogeochemical cycling response to the glacial-interglacial cycles of the late Neogene. South of the present-day position of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean, biogenic opal is generally much more abundant in sediments during interglacials compared to glacials. To the north, an anti-phased relationship is observed, with maximum opal abundance instead occurring during glacials. This antagonistic response of sedimentary properties provides an important model validation target for testing hypotheses of glacial-interglacial change against, particularly for understanding the causes of the concurrent variability in atmospheric CO 2 . Here, I illustrate a time-dependent modelling approach to helping understand climates of the past by means of the mechanistic simulation of marine sediment core records. I find that a close match between model-predicted and observed down-core changes in sedimentary opal content can be achieved when changes in seasonal sea-ice extent are imposed, whereas the predicted sedimentary response to iron fertilization on its own is not consistent with sedimentary observations. The results of this sediment record model-data comparison supports previous inferences that the changing cryosphere is the primary driver of the striking features exhibited by the paleoceanographic record of this region.

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Late-Quaternary changes in productivity of the Southern Ocean

Cited by 90 publications

References 46 publications

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios

Insights on geochemical cycling of U, Re and Mo from seasonal sampling in Boston Harbor, Massachusetts, USA

Application of sediment core modelling to interpreting the glacial-interglacial record of Southern Ocean silica cycling

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Late-Quaternary changes in productivity of the Southern Ocean

Cited by 90 publications

References 46 publications

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment 231Pa/230Th ratios

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment 231Pa/230Th ratios

Insights on geochemical cycling of U, Re and Mo from seasonal sampling in Boston Harbor, Massachusetts, USA

Application of sediment core modelling to interpreting the glacial-interglacial record of Southern Ocean silica cycling

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Product

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Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment ²³¹Pa/²³⁰Th ratios