Spring bloom dynamics in a subarctic fjord influenced by tidewater outlet glaciers (Godthåbsfjord, SW Greenland)

Abstract

In high-latitude fjord ecosystems, the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web. However, the environmental factors that control the timing and intensity of these spring blooms remain uncertain. In 2013, we studied the spring bloom dynamics in Godthåbsfjord, a large fjord system adjacent to the Greenland Ice Sheet. Our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers. A combination of out-fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring (April-May), which supplied nutrient-rich water to the surface layer. This surface water was subsequently transported out-fjord, and due to this circulation regime, the biomass accumulation of phytoplankton was displaced away from the glaciers. In late May, the upwelling weakened and the dominant wind direction changed, thus reversing the direction of the surface water transport. Warmer water was now transported toward the inner fjord, and a bloom was observed close to the glacier terminus. Overall, our findings imply that the timing, intensity, and location of the spring blooms in Godthåbsfjord are controlled by a combination of upwelling strength and wind forcing. Together with sea ice cover, the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem.

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

“…During summer, the upper stratification is maintained by runoff (estuarine circulation), subglacial freshwater discharge (subglacial circulation), and glacial ice melt. During winter the upper stratification is a result of sea ice cover and (dense) coastal inflow (Meire et al, ; Mortensen et al, ). Two circulation modes are associated with lifting of isotherms near the sea surface in the inner part of the fjord: dense coastal inflows during winter and subglacial circulation during summer, and both contribute to maintaining the 1 °C isotherm at ~20‐m depth for at least 8 years, that is, from 2008 to winter 2016.…”

“…During summer, the upper stratification is maintained by runoff (estuarine circulation), subglacial freshwater discharge (subglacial circulation), and glacial ice melt. During winter the upper stratification is a result of sea ice cover and (dense) coastal inflow (Meire et al, 2016;Mortensen et al, 2014). Two circulation modes are associated with lifting of…”

“…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.…”

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

“…Therefore, Hornsund with tidewater glaciers is particularly susceptible to the influence of glacier melting, which releases fresh meltwater and drifting ice to fjords. These processes have shown to supply modern and ancient OM, trace metals, and nutrients both directly by releasing glacier-trap resources and indirectly by exposing terrestrial landscape prone to runoff to fjord ecosystems 32,33 . (Table 3).…”

Impact of glacial meltwater on spatiotemporal distribution of copepods and their grazing impact in Young Sound NE, Greenland

“…However, recent studies from the Godthaabsfjord have shown that sub‐glacial discharge of meltwater from marine terminating glaciers results in nutrient transport up into the photic zone, producing secondary blooms in late summer (Arendt et al ; Juul‐Pedersen et al ). This indicates that the amount of fresh water and how it is delivered to the fjord (surface or sub‐surface) may influence fjord circulation nutrient availability and subsequent productivity (Mortensen et al ; Lydersen et al ; Meire et al ).…”