231Pa/230Th fractionation by ocean transport, biogenic particle flux and particle type

Siddall, Mark E.; Henderson, Gideon M.; Edwards, Neil R.; Frank, Martin; Müller, Simon; Stocker, Thomas F.; Joos, Fortunat

doi:10.1016/j.epsl.2005.05.031

Cited by 87 publications

(215 citation statements)

References 51 publications

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“…[36] The short residence time of deep waters in the Atlantic Ocean [Broecker et al, 1988] may make 231 Pa/ 230 Th ratios there less susceptible to the effects of variable productivity than in comparable areas of the Pacific or Indian Oceans [Yu et al, 1996;Marchal et al, 2000;Siddall et al, 2006]. Since 231 Pa has a longer residence time than 230 Th, 231 Pa remains available for export from an area after all 230 Th has been scavenged by particles.…”

Section: Comparison With Previous Paleoproductivity Studiesmentioning

confidence: 99%

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

et al. 2007

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The Silicic Acid Leakage Hypothesis (SALH) suggests that, during glacial periods, excess silicic acid was transported from the Southern Ocean to lower latitudes, which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric CO2. Downcore records of 230Th‐normalized opal fluxes and 231Pa/230Th ratios from seven equatorial Atlantic cores were used to reconstruct diatom productivity over the past 30 ka (where a is years) and to test the SALH. Downcore records of 231Pa/230Th ratios and opal fluxes are highly correlated, suggesting that they constitute a production‐based record of opal flux. Opal flux records support the SALH in that glacial opal burial exceeded Holocene burial by 1.8 Gt opal/ka in the area 0°–40°W and 5°N–5°S. Earlier results from the eastern equatorial Pacific Ocean showed the opposite trend, with greater Holocene than glacial opal burial, but approximately the same magnitude of difference between glacial and interglacial opal burial. We suggest four (nonexclusive) scenarios to explain the data from both basins: (1) Increased upwelling in the equatorial Atlantic and El Niño–like conditions suppressing upwelling in the eastern equatorial Pacific altered the overall nutrient supply to both basins; (2) Si leaked from the Southern Ocean because of Fe fertilization, but was prevented from upwelling in the equatorial Pacific because of El Niño–like conditions during the LGM; (3) Si leaked from the Southern Ocean because diatom productivity was limited by increased sea ice extent and was again prevented from upwelling in the equatorial Pacific; or (4) changes in ocean circulation related to the decreased input of Agulhas water to the glacial South Atlantic provided excess dissolved Si to the equatorial Atlantic Ocean. A deglacial opal pulse is seen in both the Atlantic and Pacific Oceans. All four scenarios and the presence of the common deglacial opal pulse suggest a common driver in the Southern Ocean.

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Section: Comparison With Previous Paleoproductivity Studiesmentioning

confidence: 99%

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

et al. 2007

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“…Even with such efforts, it may be that we can never truly interpret a geochemical tracer such as 231 Pa/ 230 Th simply in terms of water-mass advection. However, if we are able to understand the complex controls on the export of Pa, then model approaches to comprehensive datasets are likely to be informative as to past advection rates [64].…”

Section: (I) Salinity and Temperaturementioning

confidence: 99%

“…There are fundamental gaps in our theoretical and modelling understanding of the underlying thermodynamics that control the broad biogeochemical processes used in the palaeoceanographic community. A better understanding of processes such as particle adsorption and desorption will improve our understanding of important transport mechanisms in the ocean such as vertical scavenging [64,98].…”

Section: (Iv) Suggested Ways Forwardmentioning

confidence: 99%

“…In §1, we described how early large-scale conceptual models drove the fundamental questions for early palaeoceanographic studies [2,12]. As described in §2a, modelling is playing an important role in developing our interpretations of new palaeoceanographic proxies [62][63][64][65][66][67][68][69][70], and this type of approach characterizes one of the ways that modelling and observational techniques can be used in tandem. We have hinted at a missing link between palaeo-proxy development and a theoretical/modelling understanding of molecular/particle-scale processes [62,94,95].…”

Section: (D) Comparisons Between Modelling and Datamentioning

confidence: 99%

“…This strategy has shown considerable promise [63,64,69,71]. Another avenue for progress is the development of coupled modelling.…”

Section: (D) Comparisons Between Modelling and Datamentioning

confidence: 99%

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Palaeoceanography: motivations and challenges for the future

Robinson

Siddall

2012

Phil. Trans. R. Soc. A.

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The ocean interacts with the atmosphere, biosphere and cryosphere in a complex way, modulating climate through the storage and transport of heat, nutrients and carbon. As such, it is important that we understand the ways in which the ocean behaves and the factors that can lead to change. In order to gain this understanding, we need to look back into the past, on time scales from recent decadal-scale change, through the abrupt changes of the Pleistocene and back to times when the Earth's climate was significantly different than the Holocene. A key challenge facing the field of palaeoceanography is to combine data and modelling in a common framework. Coupling palaeo-data and models should improve our knowledge of how the Earth works, and perhaps of more direct societal relevance, might enable us to provide better predictive capabilities in climate modelling. In this discussion paper, we examine the motivations, past successes and challenges facing palaeoceanographic studies. We then suggest a number of areas and approaches that we believe will allow palaeoceanography to continue to provide new insights into processes that affect future climate change.

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Natural biogeochemical cycle of mercury in a global three‐dimensional ocean tracer model

Zhang

Jaeglé

Thompson

2014

Global Biogeochemical Cycles

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We implement mercury (Hg) biogeochemistry in the offline global 3-D ocean tracer model (OFFTRAC) to investigate the natural Hg cycle, prior to any anthropogenic input. The simulation includes three Hg tracers: dissolved elemental (Hg 0 aq ), dissolved divalent (Hg II aq ), and particle-bound mercury (Hg P aq ). Our Hg parameterization takes into account redox chemistry in ocean waters, air-sea exchange of Hg 0 , scavenging of Hg II aq onto sinking particles, and resupply of Hg II aq at depth by remineralization of sinking particles. Atmospheric boundary conditions are provided by a global simulation of the natural atmospheric Hg cycle in the GEOS-Chem model. In the surface ocean, the OFFTRAC model predicts global mean concentrations of 0.16 pM for total Hg, partitioned as 80% Hg II aq , 14% Hg 0 aq , and 6% Hg P aq . Total Hg concentrations increase to 0.38 pM in the thermocline/intermediate waters (between the mixed layer and 1000 m depth) and 0.82 pM in deep waters (below 1000 m), reflecting removal of Hg from the surface to the subsurface ocean by particle sinking followed by remineralization at depth. Our model predicts that Hg concentrations in the deep North Pacific Ocean (>2000 m) are a factor of 2-3 higher than in the deep North Atlantic Ocean. This is the result of cumulative input of Hg from particle remineralization as deep waters transit from the North Atlantic to the North Pacific on their~2000 year journey. The model is able to reproduce the relatively uniform concentrations of total Hg observed in the old deep waters of the North Pacific Ocean (observations: 1.2 ± 0.4 pM; model: 1.1 ± 0.04 pM) and Southern Ocean (observations: 1.1 ± 0.2 pM; model: 0.8 ± 0.02 pM). However, the modeled concentrations are factors of 5-6 too low compared to observed concentrations in the surface ocean and in the young water masses of the deep North Atlantic Ocean. This large underestimate for these regions implies a factor of 5-6 anthropogenic enhancement in Hg concentrations.

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231Pa/230Th fractionation by ocean transport, biogenic particle flux and particle type

Cited by 87 publications

References 51 publications

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

Palaeoceanography: motivations and challenges for the future

Natural biogeochemical cycle of mercury in a global three‐dimensional ocean tracer model

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