Abstract
ABSTRACT The estuary is dominated by sea ice and snow cover from winter to spring, and a highly turbid meltwater plume during summer. The aims were to quantify the variability in optical conditions, inorganic nutrients, and primary production between these two extremes, and identify the drivers of variability. Data were obtained during a summer cruise along a transect in the estuary in August 2007, and a spring campaign on the ice in March 2011. The study comprises conductivity, temperature, and depth (CTD), Kd(PAR), Kd(λ), PAR transmittance, photic depth, chl-a, nutrients (NO3, NO2, NH3, PO4, and SiO2), primary production, and sediment concentrations. PAR transmittance varied between 5% below snow and ice and 85% in clear water with 44% in turbid meltwater. Primary production rates were similar below the ice in March (76.8 mg C m−2 d−1) and in the highly turbid meltwater in August (94.8 mg C m−2 d−1), but higher (246.6 mg C m−2 d−1) at the mouth of the fjord. Meltwater inflow was the main driver of variability during summer and the snow and sea ice during spring. Under-ice primary production will increase three-fold with less snow on the sea ice, and the higher meltwater turbidity with increased melting of glacial ice and runoff will only reduce primary production slightly.
Highlights
A multitude of rivers in areas covered by glaciers and ice caps in Polar regions supply large amounts of fine-grained sediments with their meltwater into estuaries and fjords during summer (e.g., Hasholt et al 2012; Kuzyk et al 2008; Retamal, Bonilla, and Vincent 2008; Syvitski, Burnell, and Skei 1987)
Many of these same fjords and estuaries are covered during winter and spring by sea ice and snow (Syvitski, Burnell, and Skei 1987), which strongly attenuate light (Grenfell and Maykut 1977; Mundy, Barber, and Michel 2005; Perovich et al 1993) and thereby reduce light for photosynthesis and primary production, both within the ice and below (Lund-Hansen et al 2017)
Polar regions are in focus because of climate change (Parkinson et al 1999; Thompson 2010), because higher air temperatures will increase freshwater runoff from glaciers and ice caps (Hanna et al 2008) and thereby increase discharges of turbid meltwater into fjords and estuaries (Hasholt et al 2012)
Summary
A multitude of rivers in areas covered by glaciers and ice caps in Polar regions supply large amounts of fine-grained sediments with their meltwater into estuaries and fjords during summer (e.g., Hasholt et al 2012; Kuzyk et al 2008; Retamal, Bonilla, and Vincent 2008; Syvitski, Burnell, and Skei 1987). Many of these same fjords and estuaries are covered during winter and spring by sea ice and snow (Syvitski, Burnell, and Skei 1987), which strongly attenuate light (Grenfell and Maykut 1977; Mundy, Barber, and Michel 2005; Perovich et al 1993) and thereby reduce light for photosynthesis and primary production, both within the ice and below (Lund-Hansen et al 2017). As part of ongoing fjord and estuarine research and their climate-change responses, there is a need for reference points in the Polar regions This is here accomplished for the first time based on comparison and quantification of spring and summer optical properties, nutrient concentrations, and primary production rates in the upper parts of the water column in the same estuary (Kangerlussuaq, Greenland) using the same methods and e1414468-2
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