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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.


The locations of EPICA Dome C and Berkner Island coring locations on Antarctica.   
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f1: The locations of EPICA Dome C and Berkner Island coring locations on Antarctica.   

Mentions: Here we present high-resolution fluxes of total and soluble atmospheric Fe, as well as calculated aerosol Fe solubility, from the Last Glacial Maximum (LGM; 21–26 kyr before present (BP)) of the EPICA Dome C ice core1520 from East Antarctica (EDC; 75° 06′ S 123° 21′ E, 3,233 m.a.s.l.; Fig. 1) and from Marine Isotope Stage (MIS) 2-3 (22–52 kyr BP) from an ice core from Berkner Island (79° 32.9′ S 45° 32.9′ E; Fig. 1). Soluble Fe was determined using a novel rapid-filtration technique, in meltwater at pH ∼5.3 (the natural pH of the melted ice) or following leaching of sublimated dry dust with natural seawater, analogous to instantaneous techniques used with modern aerosols27. Our data are much more representative of dissolution of atmospheric dust in the ocean than previous ice-core studies, avoiding both unrepresentative leaching by strong acids19202223 or precipitation of insoluble Fe(III) hydroxides during melting. These methods are relevant for the possible modes of deposition of dust into the ocean, either deposition within rain, where dust has already been exposed to liquid at pH ∼5.3, or deposition of dry dust or solid ice/snow containing dust to the ocean where the first liquid encountered is seawater. We find that both total aerosol Fe fluxes and aerosol Fe solubility were very variable throughout the LGM in EDC ice (1–42% soluble; pH ∼5.3 mean 10%, median 6%) leading to highly variable soluble aerosol Fe fluxes of 0.01–0.84 mg m−2 per year at Dome C throughout the interval. At Berkner Island, although aerosol Fe solubility was lower than Dome C (mean ∼3%), higher dust fluxes resulted in similar mean soluble aerosol Fe fluxes to those at Dome C during the LGM. While these calculated soluble Fe fluxes are not fully representative of bioavailable Fe fluxes to the Southern Ocean, they enable an improved estimate of the atmospheric Fe that would have been deposited and dissolved in seawater at the LGM compared with previous studies. Our measured aerosol Fe solubilities and soluble aerosol Fe fluxes are higher than typically used in models of ocean biogeochemistry, and thus we suggest that models should consider higher and more spatially and temporally variable soluble atmospheric Fe fluxes to the Southern Ocean during glacial intervals.


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)

The locations of EPICA Dome C and Berkner Island coring locations on Antarctica.   
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: The locations of EPICA Dome C and Berkner Island coring locations on Antarctica.   
Mentions: Here we present high-resolution fluxes of total and soluble atmospheric Fe, as well as calculated aerosol Fe solubility, from the Last Glacial Maximum (LGM; 21–26 kyr before present (BP)) of the EPICA Dome C ice core1520 from East Antarctica (EDC; 75° 06′ S 123° 21′ E, 3,233 m.a.s.l.; Fig. 1) and from Marine Isotope Stage (MIS) 2-3 (22–52 kyr BP) from an ice core from Berkner Island (79° 32.9′ S 45° 32.9′ E; Fig. 1). Soluble Fe was determined using a novel rapid-filtration technique, in meltwater at pH ∼5.3 (the natural pH of the melted ice) or following leaching of sublimated dry dust with natural seawater, analogous to instantaneous techniques used with modern aerosols27. Our data are much more representative of dissolution of atmospheric dust in the ocean than previous ice-core studies, avoiding both unrepresentative leaching by strong acids19202223 or precipitation of insoluble Fe(III) hydroxides during melting. These methods are relevant for the possible modes of deposition of dust into the ocean, either deposition within rain, where dust has already been exposed to liquid at pH ∼5.3, or deposition of dry dust or solid ice/snow containing dust to the ocean where the first liquid encountered is seawater. We find that both total aerosol Fe fluxes and aerosol Fe solubility were very variable throughout the LGM in EDC ice (1–42% soluble; pH ∼5.3 mean 10%, median 6%) leading to highly variable soluble aerosol Fe fluxes of 0.01–0.84 mg m−2 per year at Dome C throughout the interval. At Berkner Island, although aerosol Fe solubility was lower than Dome C (mean ∼3%), higher dust fluxes resulted in similar mean soluble aerosol Fe fluxes to those at Dome C during the LGM. While these calculated soluble Fe fluxes are not fully representative of bioavailable Fe fluxes to the Southern Ocean, they enable an improved estimate of the atmospheric Fe that would have been deposited and dissolved in seawater at the LGM compared with previous studies. Our measured aerosol Fe solubilities and soluble aerosol Fe fluxes are higher than typically used in models of ocean biogeochemistry, and thus we suggest that models should consider higher and more spatially and temporally variable soluble atmospheric Fe fluxes to the Southern Ocean during glacial intervals.

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.