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

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 ice albedo feedback, 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 characteristics Chla, atot(443), and Kd(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.

Spatio-Temporal Variability of Suspended Particulate Matter in a High-Arctic Estuary (Adventfjorden, Svalbard) Using Sentinel-2 Time-Series

“…With the ~20 m spatial resolution achieved in our workflow on S2 data, trends in riverine inputs to the dynamic and complex nearshore zones of inaccessible Arctic fjords can be explored. Especially during the summer months, the extensive time-series dataset allows a neardaily monitoring of river plume evolution and has the potential to monitor the long-term trends, such as coastal darkening and related decrease of benthic light availability [22]. It is reasonable to believe that the calibration holds for comparable catchments in polar regions, dominated by glaciogenic sediments.…”

“…Thus, high turbidity in sediment-laden freshwater plumes and comparably high amounts of CDOM may limit light availability for coastal phytoplankton and benthic primary producers [12,19,20]. Coastal darkening [21,22] refers to this ongoing change through increased light attenuation from terrestrial inputs in coastal ecosystems, which results in decreased benthic light availability. SPM may consist of organic and inorganic material [23].…”

Drivers of change in Arctic fjord socio-ecological systems: Examples from the European Arctic

“…Meltwater from land-terminating glaciers enters the fjord at the surface, resulting in strong stratification that drives estuarine circulation. This also increases turbidity (Konik et al, 2021), which may have consequences for benthic life (5.2). At marine-terminating glaciers, freshwater input comes mostly from below as subglacial discharge, often several hundred metres below the sea surface (Hopwood et al, 2020).…”

“…Assuming the availability of necessary nutrients (4.2), this means that light plays a major role in the global carbon cycle by controlling the geographical and depth distributions of primary producers (5.1; Gattuso et al, 2020). In the Arctic, three processes linked to climate change that affect the penetration of light into the water column have been well researched: 1) Current and future projected sea-ice loss (2.1) creates longer sea-ice free periods that allows for greater penetration of light (Pavlov et al, 2019) 2) Projected increases in freshwater input (2.3) reduce light penetration in the coastal zone by increasing turbidity via the delivery of particulate and dissolved organic matter (DOM; Frigstad et al, 2020;Nowak et al, 2021) 3) If summer cloudiness increases as the Arctic warms it will decrease incident PAR above the sea surface (Bélanger et al, 2013) Largely due to increased freshwater inputs, most fjords in Western Svalbard (1997Svalbard ( -2019Konik et al, 2021), and many fjords on mainland Norway (1935Aksnes et al, 2009) have experienced a regime shift towards darker water, a phenomenon referred to as "darkening" or "browning". It is hypothesised that this darkening of water may cause a reduction to primary production (5.1; Aksnes et al, 2009).…”

“…Due largely to Atlantification (3.2), 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;Konik et al, 2021). This means that climate change may be mediating trophic shifts in fjord ecosystems, a process referred to as 'borealisation'.…”