Microplankton succession in a SW Greenland tidewater glacial fjord influenced by coastal inflows and run-off from the Greenland Ice Sheet

Abstract

Studies of annual successions and inter-annual variations in sub-Arctic and Arctic microplankton assemblages are required in order to understand the structure and function of marine ecosystems. This study depicts the microplankton ([20 lm) structure in a sub-Arctic tidewater glacial fjord system, SW Greenland. The descriptions are based on monthly net hauls collected between January 2006 and December 2010. Two blooms, with distinctive species compositions, were identified across all years: a spring bloom and a summer/autumn bloom. In addition, the winter season-with weak stratification, deep tidal mixing, and dense coastal inflows-was characterised by a separate species composition at much lower abundance. Here, the highest variety of microplankton groups was recorded and represented by diatoms (Chaetoceros spp. and Thalassiosira spp.), silicoflagellates, dinoflagellates, and ciliates. During the spring bloom, species correlated with higher light intensities, i.e. haptophytes and diatoms (Thalassiosira spp. and Fragilariopsis spp.), dominated the microplankton assemblage. Among these, diatoms were also correlated with cooler and fresher waters influenced by springtime melt. During the summer/autumn bloom, the microplankton assemblage was mainly represented by diatoms, such as Chaetoceros spp. 'Low-saline' chrysophytes were also present. The latter bloom coincides with elevated temperatures in the fjord and renewal of nutrients due to the onset of glacial meltwater run-off from the Greenland Ice Sheet. Our study shows a yearly recurrent succession of microplankton assemblages and that the annual succession is controlled primarily by ocean-fjordglacier interactions.

High export of dissolved silica from the Greenland Ice Sheet

“…Concurrent with the depletion of nutrients (DSi and nitrate) in the upper water layer, a shift in the species composition occurred and diatoms became less abundant (Figure ). The same temporal pattern is observed in the interannual phytoplankton succession at station GF3 (Figure ) which consistently shows a succession from diatoms to haptophytes in spring, coinciding with a decrease of DSi in surface water [ Juul‐Pedersen et al , ; Krawczyk et al , ] (Figure ). In summer, new nutrients are resupplied to the surface layer through subglacial freshwater discharge (Figure ).…”

Spatial and temporal distribution of planktonic protists in the East Greenland fjord and offshore waters

“…Dinobryon balticum) and the diatom Melosira arctica characterised the inner fjord waters along with the lowest recorded salinity. D. balticum is regarded as preferring low-saline summer surface waters in sub-Arctic and Arctic fjords (Hasle & Heimdal 1998, Krawczyk et al 2015. M. arctica was recorded only in inner Young Sound throughout the study and is commonly found attached to sea ice or in the plankton under or in the vicinity of ice (Hasle & Syvertsen 1996).…”

“…Strong freshwater input delivers loads of silt, carrying Si(OH) 4 to the surface waters of the inner fjord. Generally, diatoms and colonial chrysophytes are common components of sub-Arctic and Arctic summer waters (Hasle & Heimdal 1998, Okolodkov et al 2000, Krawczyk et al 2015. The low-salinity but warmer waters re corded in mid Young Sound indicate summer heating of the fresher surface waters as these waters are transported out of the fjord.…”

“…Waters here are characterised by the diatom genus Fragilariopsis and dinoflagellates. The genus Fragilariopsis is often associated with melting sea ice but also appears in ice-free, open marine waters (Hasle & Syvertsen 1996, Quillfeldt 1996, 2001, 2005 and is a (Quillfeldt 1996, 2001, Lovejoy et al 2002, Jensen 2003, Krawczyk et al 2015. The dominance of genus Fragilariopsis in mid Young Sound corresponds to melting sea ice and freshwater inputs from the inner fjord.…”

Local Coastal Water Masses Control Heat Levels in a West Greenland Tidewater Outlet Glacier Fjord

“…Temperature and salinity gradients along the fjords are regulated by the fjords' seasonal circulation systems and their various physical drivers (Mortensen et al, , ). Besides being important components for melting of the Greenland Ice Sheet (GIS) and associated global sea level rise, these seasonal circulation systems determine biological parameters: changes in fjord circulation and physical drivers seem to explain spatial gradients in metazooplankton communities (Arendt et al, ; Tang et al, ) and seasonal variations in phytoplankton species composition and primary production (Juul‐Pedersen et al, ; Krawczyk et al, ; Meire et al, ). Biogeochemical gradients generated by these circulation systems also influence the exchange of properties between fjords and the open ocean: Rysgaard et al () found that the mixing of surface water inside the fjord with coastal water masses regulated the air‐sea gas exchange of CO 2 in Godthåbsfjord during summer.…”