In:
Ocean Science, Copernicus GmbH, Vol. 19, No. 4 ( 2023-08-16), p. 1225-1252
Kurzfassung:
Abstract. The inflow of warm and saline Atlantic water to the
Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the
Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of
volume transport and is associated with a large transport of heat towards the
Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe
Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry,
a method that has been calibrated by in situ observations gathered over 2
decades. Monthly averaged surface velocity anomalies calculated from SLA
data were strongly correlated with anomalies measured by moored acoustic
Doppler current profilers (ADCPs) with consistently higher correlations when
using the reprocessed SLA data released in December 2021 rather than the
earlier version. In contrast to the earlier version, the reprocessed data
also had the correct conversion factor between sea level slope and surface
velocity required by geostrophy. Our results show that the IF inflow crosses
the IFR in two separate branches. The Icelandic branch is a jet over the
Icelandic slope with average surface speed exceeding 20 cm s−1, but it
is narrow and shallow with an average volume transport of less than 1 Sv
(106 m3 s−1). Most of the Atlantic water crosses the IFR
close to its southernmost end in the Faroese branch. Between these two
branches, water from the Icelandic branch turns back onto the ridge in a
retroflection with a recirculation over the northernmost bank on the IFR.
Combining multi-sensor in situ observations with satellite SLA data, monthly
mean volume transport of the IF inflow has been determined from January 1993
to December 2021. The IF inflow is part of the Atlantic Meridional
Overturning Circulation (AMOC), which is expected to weaken under continued
global warming. Our results show no weakening of the IF inflow. Annually
averaged volume transport of Atlantic water through the monitoring section
had a statistically significant (95 % confidence level) increasing trend
of (0.12±0.10) Sv per decade. Combined with increasing temperature,
this caused an increase of 13 % in the heat transport, relative to 0 ∘C, towards the Arctic of the IF inflow over the 29 years of
monitoring. The near-bottom layer over most of the IFR is dominated by cold
water of Arctic origin that may contribute to the overflow across the ridge.
Our observations confirm a dynamic link between the overflow and the
Atlantic water flow above. The results also provide support for a previously
posed hypothesis that this link may explain the difficulties in reproducing
observed transport variations in the IF inflow in numerical ocean models,
with consequences for its predictability under climate change.
Materialart:
Online-Ressource
ISSN:
1812-0792
DOI:
10.5194/os-19-1225-2023
Sprache:
Englisch
Verlag:
Copernicus GmbH
Publikationsdatum:
2023
ZDB Id:
2183769-7
