Glacial meltwater determines the balance between autotrophic and heterotrophic processes in a Greenland fjord

TY - JOUR

T1 - Glacial meltwater determines the balance between autotrophic and heterotrophic processes in a Greenland fjord

AU - Sejr, Mikael K.

AU - Bruhn, Annette

AU - Dalsgaard, Tage

AU - Juul-Pedersen, Thomas

AU - Stedmon, Colin A.

AU - Blicher, Martin

AU - Meire, Lorenz

AU - Mankoff, Kenneth D.

AU - Thyrring, Jakob

PY - 2022/12

Y1 - 2022/12

N2 - Global warming accelerates melting of glaciers and increases the supply of meltwater and associated inorganic particles, nutrients, and organic matter to adjacent coastal seas, but the ecosystem impact is poorly resolved and quantified. When meltwater is delivered by glacial rivers, the potential impact could be a reduction in light and nutrient availability for primary producers while supplying allochthonous carbon for heterotrophic processes, thereby tipping the net community metabolism toward heterotrophy. To test this hypothesis, we determined physical and biogeochemical parameters along a 110-km fjord transect in NE Greenland fjord, impacted by glacial meltwater from the Greenland Ice Sheet. The meltwater is delivered from glacier-fed river outlets in the inner parts of the fjord, creating a gradient in salinity and turbidity. The planktonic primary production was low, 20-45 mg C m-2 d-1, in the more turbid inner half of the fjord, increasing 10-fold to around 350 mg C m-2 d-1 in the shelf waters outside the fjord. Plankton community metabolism was measured at three stations, which displayed a transition from net heterotrophy in the inner fjord to net autotrophy in the coastal shelf waters. Respiration was significantly correlated to turbidity, with a 10-fold increase in the inner turbid part of the fjord. We estimated the changes in meltwater input and sea ice coverage in the area for the last 60 y. The long-term trend and the observed effects demonstrated the importance of freshwater runoff as a key driver of coastal ecosystem change in the Arctic with potential negative consequences for coastal productivity.

AB - Global warming accelerates melting of glaciers and increases the supply of meltwater and associated inorganic particles, nutrients, and organic matter to adjacent coastal seas, but the ecosystem impact is poorly resolved and quantified. When meltwater is delivered by glacial rivers, the potential impact could be a reduction in light and nutrient availability for primary producers while supplying allochthonous carbon for heterotrophic processes, thereby tipping the net community metabolism toward heterotrophy. To test this hypothesis, we determined physical and biogeochemical parameters along a 110-km fjord transect in NE Greenland fjord, impacted by glacial meltwater from the Greenland Ice Sheet. The meltwater is delivered from glacier-fed river outlets in the inner parts of the fjord, creating a gradient in salinity and turbidity. The planktonic primary production was low, 20-45 mg C m-2 d-1, in the more turbid inner half of the fjord, increasing 10-fold to around 350 mg C m-2 d-1 in the shelf waters outside the fjord. Plankton community metabolism was measured at three stations, which displayed a transition from net heterotrophy in the inner fjord to net autotrophy in the coastal shelf waters. Respiration was significantly correlated to turbidity, with a 10-fold increase in the inner turbid part of the fjord. We estimated the changes in meltwater input and sea ice coverage in the area for the last 60 y. The long-term trend and the observed effects demonstrated the importance of freshwater runoff as a key driver of coastal ecosystem change in the Arctic with potential negative consequences for coastal productivity.

KW - CO2

KW - Coastal ecology

KW - Greenland

KW - primary production

KW - respiration

KW - Autotrophic Processes

KW - Plankton

KW - Ecosystem

KW - Estuaries

KW - Heterotrophic Processes

KW - Ice Cover

UR - http://www.scopus.com/inward/record.url?scp=85144304087&partnerID=8YFLogxK

U2 - 10.1073/pnas.2207024119

DO - 10.1073/pnas.2207024119

M3 - Journal article

C2 - 36534802

AN - SCOPUS:85144304087

SN - 0027-8424

VL - 119

JO - Proceedings of the National Academy of Sciences

JF - Proceedings of the National Academy of Sciences

IS - 52

M1 - e2207024119

ER -