Experimentally determined temperature thresholds for Arctic plankton community metabolism

J M Holding,S Agustí,A Coello-Camba,P Wassmann,C M Duarte,J M Arrieta,R Vaquer-Sunyer

doi:10.5194/bg-10-357-2013

Abstract

Abstract. Climate warming is especially severe in the Arctic, where the average temperature is increasing 0.4 °C per decade, two to three times higher than the global average rate. Furthermore, the Arctic has lost more than half of its summer ice extent since 1980 and predictions suggest that the Arctic will be ice free in the summer as early as 2050, which could increase the rate of warming. Predictions based on the metabolic theory of ecology assume that temperature increase will enhance metabolic rates and thus both the rate of primary production and respiration will increase. However, these predictions do not consider the specific metabolic balance of the communities. We tested, experimentally, the response of Arctic plankton communities to seawater temperature spanning from 1 °C to 10 °C. Two types of communities were tested, open-ocean Arctic communities from water collected in the Barents Sea and Atlantic influenced fjord communities from water collected in the Svalbard fjord system. Metabolic rates did indeed increase as suggested by metabolic theory, however these results suggest an experimental temperature threshold of 5 °C, beyond which the metabolism of plankton communities shifts from autotrophic to heterotrophic. This threshold is also validated by field measurements across a range of temperatures which suggested a temperature 5.4 °C beyond which Arctic plankton communities switch to heterotrophy. Barents Sea communities showed a much clearer threshold response to temperature manipulations than fjord communities.

Highlights

The European Arctic Ocean is highly influenced by the North Atlantic Current which brings warm waters into the Arctic causing it to be a relatively ice free area and contributing significantly to summer ice melt (Loeng et al, 1997; Schauer et al, 2002)
The experimental results presented here show that the metabolism of the open-ocean Arctic community collected in the Barents Sea was highly sensitive to warming, whereas that of the community already growing in the Atlanticinfluenced, warm-water Arctic fjord, showed no clear relationship with experimental temperature across the 1 to 10 ◦C experimental range
We report metabolic rates, standardized for chlorophyll a, to be able to test our results against the metabolic theory, as the metabolic theory of ecology (MTE) is based on physiological processes and refers to metabolic rates per unit biomass of the same individual (Brown et al, 2004)

Summary

Introduction

The European Arctic Ocean (consisting of the Barents Sea and the Fram Strait) is highly influenced by the North Atlantic Current which brings warm waters into the Arctic causing it to be a relatively ice free area and contributing significantly to summer ice melt (Loeng et al, 1997; Schauer et al, 2002). The European Arctic is characterized by the large outflow of less saline cold waters from the north, most notably from the East Greenland and East Spitsbergen Currents that a have high solubility to CO2. These physical properties are responsible for the high CO2 uptake in the mostly ice-free Barents Sea, which is estimated to be 9 × 1012 g C yr−1 (Fransson et al, 2001), compared to the entire ice-covered Arctic interior (31 × 1012 g C yr−1; Kaltin and Anderson, 2005). High primary production supports productive fisheries (Pauly and Christensen, 1995) and contributes to the high atmospheric CO2 uptake in the North Atlantic (Takahashi et al, 2002)

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