Darkening of the Svalbard Fjords Waters Observed With Satellite Ocean Color Imagery in 1997–2019

Marta Konik,Alexey K Pavlov,Piotr Kowalczuk,Mirosław Darecki,Sławomir Sagan

doi:10.3389/fmars.2021.699318

Marta Konik, Alexey K Pavlov + Show 3 more

Open Access

https://doi.org/10.3389/fmars.2021.699318

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Abstract

Global warming is not often discussed in the context of light availability within the water column. However, the light regimes in the Arctic Ocean are controlled by three factors that are influenced by climate changes which are the sea icealbedofeedback, glacial meltwater runoff and marine primary production. Based on a satellite data series acquired during time period 1997 – 2019, we inspected long-term changes of the three commonly used optical characteristicsChla,atot(443), andKd(490) within the Svalbard fjords and on the West Spitsbergen Shelf. We revealed evident positive trends in summer (July – September) in the Isfjorden, the Kongsfjorden, the Hornsund fjord, and the Bellsund. Moreover, between 1997 and 2019 at the majority of locations we observed a regime shift toward darker waters. We showed that light availability has changed in the Svalbard fjords since 1997, which may be a symptom of transformations in the environment that should be further investigated and monitored.

Highlights

In the mid-1970s a significant change in the Arctic Ocean system began
Throughout the whole data series spanning 1997–2019, the broadest range of Chla concentration values were recorded mostly in April when phytoplankton blooms start in this region
It should be noted that the enhanced amplitudes of anomalies observed in recent years are in line with observations and models showing that growing variability in the system can precede its regime shift (Spanbauer et al, 2014; Bury et al, 2021)

Summary

Introduction

In the mid-1970s a significant change in the Arctic Ocean system began. Since systematic satellite observations have proved that the Arctic Ocean ice cover is shrinking, and in the following decades the trend has continued with a rate of −13.3% dec−1 (Serreze and Stroeve, 2015). Sea ice forms a boundary layer in polar and sub-polar marine basins, that reduces the heat, mass, and momentum exchange between the ocean and atmosphere (McPhee, 2017), alters the surface albedo and reduces radiative energy transfer to the underlying water, which affects the heating rate and primary production (Arrigo, 2017). The sea-ice decline in the Arctic Ocean has been accompanied by an increase of its productivity (Ardyna and Arrigo, 2020) that has been observed in eutrophic shelf area, oligotrophic Central Arctic Basin and exchange gateways in Bering and Fram Straits (Kohler et al, 2007) and Canadian Archipelago (Hill et al, 2018). The Fram Strait, the Arctic Ocean received steadily increased advection of heat and salt from mid-latitudes with inflowing Atlantic Water (Walczowski, 2014; Polyakov et al, 2017). Together with the inflow of warm and salty Atlantic Water a significant northward advance of temperate phytoplankton and changes of the planktonic organism size distribution toward smaller organisms, i.e., pico- and nanoplankton have been observed (Oziel et al, 2017; Neukermans et al, 2018)

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