TY - JOUR

T1 - Variability and decadal trends in the Isfjorden (Svalbard) ocean climate and circulation - an indicator for climate change in the European Arctic

AU - R. Skogseth,

AU - Иванов, Борис Вячеславович

PY - 2020/8/1

Y1 - 2020/8/1

N2 - Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord's climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SST w/VT w: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr −1) and summer (SST S/VT S: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr −1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr −1) and summer (0.7 ± 0.1 °C 10 yr −1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr −1) and summer (0.07 ± 0.05 10 yr −1) suggest increased AW advection as a main reason for Isfjorden's climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord's impact on the local terrestrial climate. In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

AB - Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord's climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SST w/VT w: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr −1) and summer (SST S/VT S: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr −1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr −1) and summer (0.7 ± 0.1 °C 10 yr −1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr −1) and summer (0.07 ± 0.05 10 yr −1) suggest increased AW advection as a main reason for Isfjorden's climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord's impact on the local terrestrial climate. In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

KW - Arctic Ocean, Svalbard, West Spitsbergen Shelf, Isfjorden

KW - Atlantic Water intrusion

KW - Nearshore dynamics

KW - Ocean circulation and currents

KW - Oceanography

KW - Tides, surges and sea level

KW - TSD distribution, water masses and circulation

KW - FJORD

KW - SEA-ICE COVER

KW - Arctic Ocean, Svalbard, West Spitsbergen Shelf

KW - Isfjorden

KW - ADVENTFJORDEN

KW - KONGSFJORDEN

KW - HEAT DELIVERY

KW - DRIVEN

KW - INFLOW

KW - ATLANTIC WATER

KW - WEST SPITSBERGEN

KW - SHELF

UR - http://www.scopus.com/inward/record.url?scp=85087589374&partnerID=8YFLogxK

U2 - https://doi.org/10.1016/j.pocean.2020.102394

DO - https://doi.org/10.1016/j.pocean.2020.102394

M3 - Article

VL - 187

JO - Progress in Oceanography

JF - Progress in Oceanography

SN - 0079-6611

M1 - 102394

ER -