The polar ocean and glacial cycles in atmospheric CO2 concentration

Sigman, Daniel M.; Hain, Mathis P.; Haug, Gerald H.

doi:10.1038/nature09149

Cited by 722 publications

(790 citation statements)

References 98 publications

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“…These results complement the available deep ocean δ 13 C data which did not clearly show a major change of NADW ventilation with the intensification of NHG (e.g., Raymo et al, 1992;Haug and Tiedemann, 1998). We propose that the increase in the formation of newly ventilated and nutrient-depleted deep waters of the Nordic Seas may have helped to maintain an enhanced ventilation of the Atlantic Ocean and in turn a strong biological pump in the global ocean (e.g., Sigman et al, 2010). This was crucial notably during a time of major reduction in Antarctic-sourced ventilation of the deep ocean over the ∼ 2.7 Ma transition (Hodell and Venz-Curtis, 2006).…”

Section: Resultssupporting

confidence: 84%

A major change in North Atlantic deep water circulation 1.6 million years ago

Khélifi

2014

Clim. Past

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Abstract. The global ocean-climate system has been highly sensitive to the formation and advection of deep overflow water from the Nordic Seas as integral part of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution over the Pliocene-Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters that were involved in driving overturning throughout the Pliocene-Pleistocene climate transitions are not well constrained. Here we investigate the evolution of a substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic neodymium isotope (ε Nd ) variability obtained from three sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths between 2170 and 5050 m in the northeast Atlantic. We find that prior to the onset of major Northern Hemisphere glaciation (NHG) ∼ 3 million years ago (Ma), ε Nd values primarily oscillated between −9 and −11 at all sites, consistent with enhanced vertical mixing and weak stratification of the water masses during the warmer-than-today Pliocene period. From 2.7 Ma to ∼ 2.0 Ma, the ε Nd signatures of the water masses gradually became more distinct, which documents a significant advection of Nordic Seas overflow deep water coincident with the intensification of NHG. Most markedly, however, at ∼ 1.6 Ma the interglacial ε Nd signatures at sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.) synchronously and permanently shifted by 2 to 3 ε Nd units to less radiogenic values, respectively. Since then the difference between glacial and interglacial ε Nd values has been similar to the Late Quaternary at each site. A decrease of ∼ 2 ε Nd units at 1.6 Ma was also recorded for the deepest water masses by site 900 (∼ 5 050 m w.d.), which thereafter, however, evolved to more radiogenic values again until the present. This major ε Nd change across the 1.6 Ma transition reflects a significant reorganization of the overturning circulation in the northeast Atlantic paving the way for the more stratified water column with distinct water masses prevailing thereafter.

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Section: Resultssupporting

confidence: 84%

A major change in North Atlantic deep water circulation 1.6 million years ago

Khélifi

2014

Clim. Past

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“…As a stronger glacial Fe supply inducing an intensified nutrient utilization is one of the potential explanations for the strengthening of Southern Ocean CO 2 uptake in glacial periods [Sigman et al, 2010], understanding Fe accumulation in sea ice, its release in the ocean by melting sea ice, and Fe bioavailability for phytoplankton, remains one of the crucial questions of present-day sea ice biogeochemistry.…”

Section: Trace Metalsmentioning

confidence: 99%

“…Future changes in the polar seas and continued sea ice retreat [Arzel et al, 2006] will affect future marine biogeochemistry, with important feedbacks on climate and consequences for marine ecosystems, some of which have already been observed [e.g., Montes-Hugo et al, 2009;Wassmann et al, 2011]. Paleo-climate studies indicate that past climatic and atmospheric composition changes were associated with extensive modifications in the polar oceans, in terms of circulation, sea ice cover and chemical composition [Crosta et al, 1998;Sarnthein et al, 2003;de Vernal et al, 2005;Sigman et al, 2010]. While a seasonal ice cover should subsist in the future [Armour et al, 2011], the future large-scale biogeochemical dynamics of the polar oceans and in particular the contribution of sea ice are difficult to predict.…”

Section: Introductionmentioning

confidence: 99%

“…The solubility pump is the ensemble of physical and chemical processes driving CO 2 dissolution and outgassing. The biological pump is driven by (i) the fixation of inorganic carbon into organic matter and its export to depth by sinking plankton material and (ii) the formation of calcium carbonate (CaCO 3 ) via calcification, releasing CO 2 [Sigman et al, 2010]. While the natural carbon cycle is largely driven by the biological pump [Sarmiento and Gruber, 2006], the uptake of anthropogenic carbon can be, so far, almost entirely explained by physical and chemical processes [Prentice et al, 2001].…”

Section: Introductionmentioning

confidence: 99%

“…Finally, iron concentrations in sea ice can be much higher than in the ocean and sea ice can act as a seasonal reservoir in the Southern Ocean [Lannuzel et al, 2007;2011]: growing sea ice incorporates large amounts of iron, later released into surface waters when the ice melts. This seasonal process may temporarily relieve iron limitation on phytoplankton growth, notably in the Southern Ocean [Lancelot et al, 2009], a key player in the marine carbon cycle [Sarmiento and Gruber, 2006;Sigman et al, 2010], but also in the Bering Sea [Aguilar-Islas et al, 2008] Sea ice proxies integrate information from biological, chemical and physical processes occurring in the polar oceans in an attempt to reconstruct past sea ice conditions [see Armand and Leventer, 2010, for a review]. Many sea ice proxies rely on assumptions related to the biogeochemical properties of the polar oceans, as recorded in marine sediment or glacial ice cores.…”

Section: Introductionmentioning

confidence: 99%

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Role of sea ice in global biogeochemical cycles: emerging views and challenges

Vancoppenolle

Meiners

Michel

et al. 2013

Quaternary Science Reviews

215

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International audienceObservations from the last decade suggest an important role of sea ice in the global biogeochemical cycles, promoted by (i) active biological and chemical processes within the sea ice; (ii) fluid and gas exchanges at the sea ice interface through an often permeable sea ice cover; and (iii) tight physical, biological and chemical interactions between the sea ice, the ocean and the atmosphere. Photosynthetic micro-organisms in sea ice thrive in liquid brine inclusions encased in a pure ice matrix, where they find suitable light and nutrient levels. They extend the production season, provide a winter and early spring food source, and contribute to organic carbon export to depth. Under-ice and ice edge phytoplankton blooms occur when ice retreats, favoured by increasing light, stratification, and by the release of material into the water column. In particular, the release of iron - highly concentrated in sea ice - could have large effects in the iron-limited Southern Ocean. The export of inorganic carbon transport by brine sinking below the mixed layer, calcium carbonate precipitation in sea ice, as well as active ice-atmosphere carbon dioxide (CO₂) fluxes, could play a central role in the marine carbon cycle. Sea ice processes could also significantly contribute to the sulphur cycle through the large production by ice algae of dimethylsulfoniopropionate (DMSP), the precursor of sulphate aerosols, which as cloud condensation nuclei have a potential cooling effect on the planet. Finally, the sea ice zone supports significant ocean-atmosphere methane (CH₄) fluxes, while saline ice surfaces activate springtime atmospheric bromine chemistry, setting ground for tropospheric ozone depletion events observed near both poles. All these mechanisms are generally known, but neither precisely understood nor quantified at large scales. As polar regions are rapidly changing, understanding the large-scale polar marine biogeochemical processes and their future evolution is of high priority. Earth system models should in this context prove essential, but they currently represent sea ice as biologically and chemically inert. Palaeoclimatic proxies are also relevant, in particular the sea ice proxies, inferring past sea ice conditions from glacial and marine sediment core records and providing analogues for future changes. Being highly constrained by marine biogeochemistry, sea ice proxies would not only contribute to but also benefit from a better understanding of polar marine biogeochemical cycles

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Global constraints on net primary production and inorganic carbon supply during glacial and interglacial cycles

et al. 2013

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.[1] Relaxation-type models have good skill at reproducing glacial-interglacial transitions in climatic variables. Here we propose a simple two-box and two-state relaxation-type model for the upper ocean (surface and permanent thermocline layers) where dissolved inorganic carbon/nutrients are supplied by the deep ocean and through remineralization within the upper ocean. The model is tuned using genetic algorithms to simulate the atmospheric CO 2 time series for the last four glacial-interglacial cycles. The fit to the data is very good, with correlations above 0.8, as the upper ocean responds to shifts in (1) the intensity of the meridional overturning circulation, from off to on during the glacial-interglacial transition, and (2) the size and sign of net primary production, with respiration greatly exceeding primary production during interglacial periods and production larger than respiration during the glacial phase. The glacial-interglacial transitions are interpreted as shifts between two distinct metabolic states of the Earth system, with high/low supply of dissolved inorganic carbon and nutrients to the productive upper ocean during interglacial/glacial periods.Citation: Pelegrı´, J. L., P. De La Fuente, R. Olivella, and A. Garcı´a-Olivares (2013), Global constraints on net primary production and inorganic carbon supply during glacial and interglacial cycles, Paleoceanography, 28, 713-725,

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The polar ocean and glacial cycles in atmospheric CO2 concentration

Cited by 722 publications

References 98 publications

A major change in North Atlantic deep water circulation 1.6 million years ago

A major change in North Atlantic deep water circulation 1.6 million years ago

Role of sea ice in global biogeochemical cycles: emerging views and challenges

Global constraints on net primary production and inorganic carbon supply during glacial and interglacial cycles

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