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The island mass effect and biological carbon uptake for the subantarctic Crozet Archipelago

The island mass effect and biological carbon uptake for the subantarctic Crozet Archipelago
The island mass effect and biological carbon uptake for the subantarctic Crozet Archipelago
Marine productivity is often higher downstream than upstream of islands. This so-called island mass effect was tested and quantified with respect to biological carbon uptake and air–sea exchange of carbon dioxide (CO2) at the Crozet Plateau between November 2004 and January 2005 during two CROZEX cruises. The remote plateau is situated at 45.5–47.0°S 49.0–53.0°E, south of the Subantarctic Front (SAF) in the Polar Frontal Zone (PFZ). Surface waters upstream (south) of the plateau had high nutrient and low chlorophyll (HNLC) concentrations. The fugacity of carbon dioxide (fCO2) in surface water was just below the atmospheric value and oceanic CO2 uptake was small (0.2±0.1 mol m?2) throughout CROZEX. The mixed-layer concentration of dissolved inorganic carbon (DIC) decreased by 15 ?mol kg?1 from November to January in these HNLC waters, indicating significant biological carbon uptake. Extensive phytoplankton blooms occurred downstream (north) of the plateau in austral spring. These reduced surface water fCO2 by 30–70 ?atm and DIC by 30–60 ?mol kg?1 and created an important oceanic sink for atmospheric CO2 of 0.6–0.8±0.4 mol m?2, corresponding to a total uptake of 1.3±0.8 Tg C (1 Tg=1012 g). The reduction of DIC in the upper 100 m was much larger downstream (2–3 mol m?2) than upstream (1 mol m?2) of the plateau in January, further confirming the existence of the island mass effect for the Crozet Archipelago. An additional finding is the sizeable DIC deficit in the HNLC waters upstream (south) of the plateau, suggesting that some HNLC waters of the PFZ are more productive than commonly thought. Deep mixed layers of 60–90 m may hide such sustained, modest marine productivity from detection by satellite.
Carbon dioxide, Island mass effect, Iron supply, Crozet Archipelago, Subantarctic Front, Polar Frontal Zone, Antarctic Circumpolar Current, Southern Ocean rent, Southern Ocean
0967-0645
2174-2190
Bakker, D.C.E.
bd373973-6b47-4d3c-ae49-4f6d894ad660
Nielsdottir, M.C.
1275379e-0f08-45cc-8d4b-e9826dda023e
Morris, P.J.
efc0a494-3d80-4116-8010-c2dd5d1bbdee
Venables, H.J.
721e7956-ccd4-48f5-be70-5bc035b52bb3
Watson, A.J.
22b78032-6022-4ed3-bea8-d1bfefcf599c
Bakker, D.C.E.
bd373973-6b47-4d3c-ae49-4f6d894ad660
Nielsdottir, M.C.
1275379e-0f08-45cc-8d4b-e9826dda023e
Morris, P.J.
efc0a494-3d80-4116-8010-c2dd5d1bbdee
Venables, H.J.
721e7956-ccd4-48f5-be70-5bc035b52bb3
Watson, A.J.
22b78032-6022-4ed3-bea8-d1bfefcf599c

Bakker, D.C.E., Nielsdottir, M.C., Morris, P.J., Venables, H.J. and Watson, A.J. (2007) The island mass effect and biological carbon uptake for the subantarctic Crozet Archipelago. Deep Sea Research Part II: Topical Studies in Oceanography, 54 (18-20), 2174-2190. (doi:10.1016/j.dsr2.2007.06.009).

Record type: Article

Abstract

Marine productivity is often higher downstream than upstream of islands. This so-called island mass effect was tested and quantified with respect to biological carbon uptake and air–sea exchange of carbon dioxide (CO2) at the Crozet Plateau between November 2004 and January 2005 during two CROZEX cruises. The remote plateau is situated at 45.5–47.0°S 49.0–53.0°E, south of the Subantarctic Front (SAF) in the Polar Frontal Zone (PFZ). Surface waters upstream (south) of the plateau had high nutrient and low chlorophyll (HNLC) concentrations. The fugacity of carbon dioxide (fCO2) in surface water was just below the atmospheric value and oceanic CO2 uptake was small (0.2±0.1 mol m?2) throughout CROZEX. The mixed-layer concentration of dissolved inorganic carbon (DIC) decreased by 15 ?mol kg?1 from November to January in these HNLC waters, indicating significant biological carbon uptake. Extensive phytoplankton blooms occurred downstream (north) of the plateau in austral spring. These reduced surface water fCO2 by 30–70 ?atm and DIC by 30–60 ?mol kg?1 and created an important oceanic sink for atmospheric CO2 of 0.6–0.8±0.4 mol m?2, corresponding to a total uptake of 1.3±0.8 Tg C (1 Tg=1012 g). The reduction of DIC in the upper 100 m was much larger downstream (2–3 mol m?2) than upstream (1 mol m?2) of the plateau in January, further confirming the existence of the island mass effect for the Crozet Archipelago. An additional finding is the sizeable DIC deficit in the HNLC waters upstream (south) of the plateau, suggesting that some HNLC waters of the PFZ are more productive than commonly thought. Deep mixed layers of 60–90 m may hide such sustained, modest marine productivity from detection by satellite.

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More information

Published date: 2007
Keywords: Carbon dioxide, Island mass effect, Iron supply, Crozet Archipelago, Subantarctic Front, Polar Frontal Zone, Antarctic Circumpolar Current, Southern Ocean rent, Southern Ocean

Identifiers

Local EPrints ID: 49517
URI: https://eprints.soton.ac.uk/id/eprint/49517
ISSN: 0967-0645
PURE UUID: f6903d58-e227-415c-bad6-c9a6f7fb6acb

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Date deposited: 12 Nov 2007
Last modified: 13 Mar 2019 20:54

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