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Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula

Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula
Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula

Nutrient supply, uptake and cycling underpin high primary productivity over the continental shelf of the west Antarctic Peninsula (WAP). Here we use a suite of biogeochemical and isotopic data collected over five years in northern Marguerite Bay to examine these macronutrient dynamics and their controlling biological and physical processes in the WAP coastal ocean. We show pronounced nutrient drawdown over the summer months by primary production which drives a net seasonal nitrate uptake of 1.83 mol N m-2 yr-1, equivalent to net carbon uptake of 146 g C m-2 yr-1. High primary production fuelled primarily by deep-sourced macronutrients is diatom-dominated, but non-siliceous phytoplankton also play a role. Strong nutrient drawdown in the uppermost surface ocean has the potential to cause transient nitrogen limitation before nutrient resupply and/or regeneration. Interannual variability in nutrient utilisation corresponds to winter sea ice duration and the degree of upper ocean mixing, implying susceptibility to physical climate change. The nitrogen isotope composition of nitrate (δ15NNO3) shows a utilisation signal during the growing seasons with a community-level net isotope effect of 4.19 ± 0.29‰. We also observe significant deviation of our data from modelled and observed utilisation trends, and argue that this is driven primarily by water column nitrification and meltwater dilution of surface nitrate. This study is important because it provides a detailed description of the nutrient biogeochemistry underlying high primary productivity at the WAP, and shows that surface ocean nutrient inventories in the Antarctic sea ice zone can be affected by intense recycling in the water column, meltwater dilution and sea ice processes, in addition to utilisation in the upper ocean.

Circumpolar Deep Water, Nitrification, Nitrogen isotopes, Nitrogen recycling, Nutrient cycles, Nutrient utilisation, Phytoplankton, Primary production, Sea ice
0967-0645
58-76
Henley, Sian F.
cd7c7f77-8494-46ad-98a9-08907fa6e06b
Tuerena, Robyn E.
c555b076-1072-4702-94ba-2f4292ff032e
Annett, Amber L.
de404d72-7e90-4dbd-884a-1df813808276
Fallick, Anthony E.
71f30e9d-8d68-426a-a5c4-d97eab78b888
Meredith, Michael P.
25fd5f1c-f3ed-40a2-af59-5a7074a25fcd
Venables, Hugh J.
ed72170e-cf1b-4b38-b5e8-d3eed65cdb06
Clarke, Andrew
b54fba97-b95a-4a17-86d6-c2bb0f1d10e3
Ganeshram, Raja S.
108fdc69-5502-4b6f-922f-dd12b398e267
Henley, Sian F.
cd7c7f77-8494-46ad-98a9-08907fa6e06b
Tuerena, Robyn E.
c555b076-1072-4702-94ba-2f4292ff032e
Annett, Amber L.
de404d72-7e90-4dbd-884a-1df813808276
Fallick, Anthony E.
71f30e9d-8d68-426a-a5c4-d97eab78b888
Meredith, Michael P.
25fd5f1c-f3ed-40a2-af59-5a7074a25fcd
Venables, Hugh J.
ed72170e-cf1b-4b38-b5e8-d3eed65cdb06
Clarke, Andrew
b54fba97-b95a-4a17-86d6-c2bb0f1d10e3
Ganeshram, Raja S.
108fdc69-5502-4b6f-922f-dd12b398e267

Henley, Sian F., Tuerena, Robyn E., Annett, Amber L., Fallick, Anthony E., Meredith, Michael P., Venables, Hugh J., Clarke, Andrew and Ganeshram, Raja S. (2017) Macronutrient supply, uptake and recycling in the coastal ocean of the west Antarctic Peninsula. Deep Sea Research Part II: Topical Studies in Oceanography, 139, 58-76. (doi:10.1016/j.dsr2.2016.10.003).

Record type: Article

Abstract

Nutrient supply, uptake and cycling underpin high primary productivity over the continental shelf of the west Antarctic Peninsula (WAP). Here we use a suite of biogeochemical and isotopic data collected over five years in northern Marguerite Bay to examine these macronutrient dynamics and their controlling biological and physical processes in the WAP coastal ocean. We show pronounced nutrient drawdown over the summer months by primary production which drives a net seasonal nitrate uptake of 1.83 mol N m-2 yr-1, equivalent to net carbon uptake of 146 g C m-2 yr-1. High primary production fuelled primarily by deep-sourced macronutrients is diatom-dominated, but non-siliceous phytoplankton also play a role. Strong nutrient drawdown in the uppermost surface ocean has the potential to cause transient nitrogen limitation before nutrient resupply and/or regeneration. Interannual variability in nutrient utilisation corresponds to winter sea ice duration and the degree of upper ocean mixing, implying susceptibility to physical climate change. The nitrogen isotope composition of nitrate (δ15NNO3) shows a utilisation signal during the growing seasons with a community-level net isotope effect of 4.19 ± 0.29‰. We also observe significant deviation of our data from modelled and observed utilisation trends, and argue that this is driven primarily by water column nitrification and meltwater dilution of surface nitrate. This study is important because it provides a detailed description of the nutrient biogeochemistry underlying high primary productivity at the WAP, and shows that surface ocean nutrient inventories in the Antarctic sea ice zone can be affected by intense recycling in the water column, meltwater dilution and sea ice processes, in addition to utilisation in the upper ocean.

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e-pub ahead of print date: 13 October 2016
Published date: 1 May 2017
Keywords: Circumpolar Deep Water, Nitrification, Nitrogen isotopes, Nitrogen recycling, Nutrient cycles, Nutrient utilisation, Phytoplankton, Primary production, Sea ice

Identifiers

Local EPrints ID: 418527
URI: https://eprints.soton.ac.uk/id/eprint/418527
ISSN: 0967-0645
PURE UUID: 6d587d07-dfc3-4142-934a-f14fa807c6ed
ORCID for Amber L. Annett: ORCID iD orcid.org/0000-0002-3730-2438

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Date deposited: 09 Mar 2018 17:31
Last modified: 10 Dec 2019 01:26

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