Terrestrial Inputs Drive Seasonality in Organic Matter and Nutrient Biogeochemistry in a High Arctic Fjord System (Isfjorden, Svalbard)

Maeve McGovern,Mats A. Granskog,Eva Leu,Amanda E. Poste,Janne E. Søreide,Alexey K. Pavlov,Anne Deininger

doi:10.3389/fmars.2020.542563

Abstract

Climate-change driven increases in temperature and precipitation are leading to increased discharge of freshwater and terrestrial material to Arctic coastal ecosystems. These inputs bring sediments, nutrients and organic matter (OM) across the land-ocean interface with a range of implications for coastal ecosystems and biogeochemical cycling. To investigate responses to terrestrial inputs, physicochemical conditions were characterized in a river- and glacier-influenced Arctic fjord system (Isfjorden, Svalbard) from May to August in 2018 and 2019. Our observations revealed a pervasive freshwater footprint in the inner fjord arms, the geochemical properties of which varied spatially and seasonally as the melt season progressed. In June, during the spring freshet, rivers were a source of dissolved organic carbon (DOC; with concentrations up to 1410 μmol L-1). In August, permafrost and glacial-fed meltwater was a source of inorganic nutrients including NO2+NO3, with concentrations 12-fold higher in the rivers than in the fjord. While marine OM dominated in May following the spring phytoplankton bloom, terrestrial OM was present throughout Isfjorden in June and August. Results suggest that enhanced land-ocean connectivity could lead to profound changes in the biogeochemistry and ecology of Svalbard fjords. Given the anticipated warming and associated increases in precipitation, permafrost thaw and freshwater discharge, our results highlight the need for more detailed seasonal field sampling in small Arctic catchments and receiving aquatic systems.

Highlights

Recent climate change driven increases in air temperature and precipitation are changing the timing, magnitude and geochemical nature of freshwater runoff with unknown implications for Arctic coastal waters
Despite the rapid warming documented in the high Arctic (IPCC, 2014; Adakudlu et al, 2019), little is known regarding how these changes will affect the quantity and quality of materials transported to and through near-shore, fjord and coastal systems and their potential impacts on local and regional biogeochemical cycles (Parmentier et al, 2017). To address these knowledge gaps, we studied the impacts of inputs from marine terminating glaciers and rivers on light, stratification, nutrient and organic matter (OM) dynamics in Isfjorden (Svalbard)
In Isfjorden, the main source of freshwater is from melting marine-terminating glaciers, and river runoff sustained by land-terminating glacial meltwater and snow melt (Nilsen et al, 2008)

Summary

Introduction

Recent climate change driven increases in air temperature and precipitation are changing the timing, magnitude and geochemical nature of freshwater runoff with unknown implications for Arctic coastal waters. The permafrost active layer is deepest in August (Christiansen et al, 2005), a typically low discharge period (Hodson et al, 2016) when glacial-meltwater has higher residence time in the catchment. Seasonal changes in catchment hydrology have implications for the transport and bioavailability of carbon and nutrients in glacial meltwater on Svalbard (Nowak and Hodson, 2015; Koziol et al, 2019) and elsewhere in the Arctic (Neff et al, 2006; Holmes et al, 2008; Spencer et al, 2008)

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Conclusion