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Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum.

Conway TM, Wolff EW, Röthlisberger R, Mulvaney R, Elderfield HE - Nat Commun (2015)

Bottom Line: Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores.Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models.Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK [2] British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.

ABSTRACT
Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

No MeSH data available.


Related in: MedlinePlus

Direct comparison of different parameters as proxies for aerosol Fe in ice cores.Total Fe concentration, in EDC ice of LGM age (left panel) and Berkner Island (BI) ice from MIS 2–3 (right panel), is shown plotted against (a) nss-Ca and total Ca concentration, (b) total Al concentration and (c) pH ∼5.3 dissolved Fe concentration. Best-fit linear regression lines with r2 values are shown. Data points represent two measurements of a single sample, and errors are smaller than the size of points.
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f5: Direct comparison of different parameters as proxies for aerosol Fe in ice cores.Total Fe concentration, in EDC ice of LGM age (left panel) and Berkner Island (BI) ice from MIS 2–3 (right panel), is shown plotted against (a) nss-Ca and total Ca concentration, (b) total Al concentration and (c) pH ∼5.3 dissolved Fe concentration. Best-fit linear regression lines with r2 values are shown. Data points represent two measurements of a single sample, and errors are smaller than the size of points.

Mentions: Our data also allow evaluation of the use of other proxies for ice core Fe (Fig. 5). We find that both nss-Ca11 (Ca with Na-calculated seasalt component removed) and total Al are good proxies for the flux of total Fe (Fig. 5). However, taking the EDC dust flux and calculating total Fe concentrations, assuming a constant crustal Fe percentage of ∼4% in dust18 underestimates total Fe for EDC samples, which are enriched in Fe (mean 8 wt%; Supplementary Data) compared with crustal values of 2–3% (ref. 36) or Patagonian topsoil (2–6%; ref. 37). EDC samples are similarly enriched for Al (mean 15 wt%; Supplementary Data), compared with crustal values of 8% (ref. 36) and Patagonian topsoil of 6–10% (ref. 37). This difference in the dust composition presumably relates to compositional-fractionation processes during transport, such as relative enrichment in silicate minerals, such as clays and feldspars33. As such, changes in composition and mineralogy may be spatially variable and site specific for ice-coring locations, complicating efforts to use dust, Ca or Al fluxes as proxies for total Fe. In addition, despite the possible usefulness of these proxies for providing information about timing and magnitude of changes in atmospheric Fe11, the lack of relationship between total and soluble Fe (Fig. 5c) means that they do not approximate soluble or bioavailable Fe. Instead, direct measurements of soluble Fe, together with biological experiments, are needed for constraining changes in soluble and bioavailable Fe supply to the oceans during climatic change and especially within stable climate intervals. However, we do note the strong covariance between ice-core dust and Fe fluxes and both Sub-Antarctic productivity and heavier Sub-Antarctic surface nitrogen isotope ratios (indicative of increased nutrient utilization) during the last 160 kyr (ref. 13), as well as a similar covariance between ice-core dust and (pH 1) Fe fluxes, sediment Fe mass accumulation rates and Sub-Antarctic export productivity over the last eight glacial cycles538; these relationships suggest that both dust or (pH 1 leached) EDC ice-core Fe fluxes do capture the order of magnitude changes in Fe supply to the Southern Ocean that are important for understanding millennial-scale climate and pCO2 variability.


Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum.

Conway TM, Wolff EW, Röthlisberger R, Mulvaney R, Elderfield HE - Nat Commun (2015)

Direct comparison of different parameters as proxies for aerosol Fe in ice cores.Total Fe concentration, in EDC ice of LGM age (left panel) and Berkner Island (BI) ice from MIS 2–3 (right panel), is shown plotted against (a) nss-Ca and total Ca concentration, (b) total Al concentration and (c) pH ∼5.3 dissolved Fe concentration. Best-fit linear regression lines with r2 values are shown. Data points represent two measurements of a single sample, and errors are smaller than the size of points.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525188&req=5

f5: Direct comparison of different parameters as proxies for aerosol Fe in ice cores.Total Fe concentration, in EDC ice of LGM age (left panel) and Berkner Island (BI) ice from MIS 2–3 (right panel), is shown plotted against (a) nss-Ca and total Ca concentration, (b) total Al concentration and (c) pH ∼5.3 dissolved Fe concentration. Best-fit linear regression lines with r2 values are shown. Data points represent two measurements of a single sample, and errors are smaller than the size of points.
Mentions: Our data also allow evaluation of the use of other proxies for ice core Fe (Fig. 5). We find that both nss-Ca11 (Ca with Na-calculated seasalt component removed) and total Al are good proxies for the flux of total Fe (Fig. 5). However, taking the EDC dust flux and calculating total Fe concentrations, assuming a constant crustal Fe percentage of ∼4% in dust18 underestimates total Fe for EDC samples, which are enriched in Fe (mean 8 wt%; Supplementary Data) compared with crustal values of 2–3% (ref. 36) or Patagonian topsoil (2–6%; ref. 37). EDC samples are similarly enriched for Al (mean 15 wt%; Supplementary Data), compared with crustal values of 8% (ref. 36) and Patagonian topsoil of 6–10% (ref. 37). This difference in the dust composition presumably relates to compositional-fractionation processes during transport, such as relative enrichment in silicate minerals, such as clays and feldspars33. As such, changes in composition and mineralogy may be spatially variable and site specific for ice-coring locations, complicating efforts to use dust, Ca or Al fluxes as proxies for total Fe. In addition, despite the possible usefulness of these proxies for providing information about timing and magnitude of changes in atmospheric Fe11, the lack of relationship between total and soluble Fe (Fig. 5c) means that they do not approximate soluble or bioavailable Fe. Instead, direct measurements of soluble Fe, together with biological experiments, are needed for constraining changes in soluble and bioavailable Fe supply to the oceans during climatic change and especially within stable climate intervals. However, we do note the strong covariance between ice-core dust and Fe fluxes and both Sub-Antarctic productivity and heavier Sub-Antarctic surface nitrogen isotope ratios (indicative of increased nutrient utilization) during the last 160 kyr (ref. 13), as well as a similar covariance between ice-core dust and (pH 1) Fe fluxes, sediment Fe mass accumulation rates and Sub-Antarctic export productivity over the last eight glacial cycles538; these relationships suggest that both dust or (pH 1 leached) EDC ice-core Fe fluxes do capture the order of magnitude changes in Fe supply to the Southern Ocean that are important for understanding millennial-scale climate and pCO2 variability.

Bottom Line: Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores.Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models.Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK [2] British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK.

ABSTRACT
Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

No MeSH data available.


Related in: MedlinePlus