Geoscience Reference
In-Depth Information
Keywords Oceanography in the Arctic Ocean and surrounding seas
Mean
dynamic topography
Surface current
GOCE satellite
1 Introduction
Changes in the dynamic topography and ocean circulation between the northern Atlantic
Ocean and the Arctic Ocean result from variations in the atmospheric forcing field and
convective overturning combined with changes in freshwater runoff and their pathways, mean
sea level, sea ice deformation and water mass transformation. The ocean circulation in this
region has been subject to investigations since Helland-Hansen and Nansen (
1909
). In gen-
eral, it can be characterized by four regional circulation regimes and cross-regional exchanges
and volume transports, namely the Northeast Atlantic, the Labrador Sea and Canadian
archipelago, the Nordic and Barents Seas and the Arctic Ocean, as illustrated in Fig.
1
.
Accurate knowledge of the ocean transport variability together with understanding of
the water mass transformations within and across these regions is highly needed to quantify
changes in the overturning circulation with acceptable uncertainty. The Atlantic meridional
overturning circulation is, among other factors, influenced by: variations in the upper ocean
and sea ice interaction; ice sheet mass changes and their effect on the regional sea-level
change; changes in freshwater fluxes and pathways; and variability in the large-scale
atmospheric pressure field. For instance, changes in the pathways of the freshwater from
the Eurasian runoff forced by shifts in the Arctic Oscillation can lead to increased trapping
of freshwater in the Arctic Ocean as presented by Morison et al. (
2012
) that, in turn, may
alter the thermohaline circulation in the sub-Arctic Seas.
Using a new combination of the ice cloud and land elevation satellite (ICESat) laser
altimeter and the gravity recovery and climate experiment (GRACE) satellites, along with
traditional hydrography, Morison et al. (
2012
) were able to show that the dominant
freshwater changes from 2005 to 2008 were an increase in surface freshwater in the
Canada basin balanced by a decrease in the Eurasian basin. These changes were due to a
cyclonic (anticlockwise) shift in the ocean pathway of the Eurasian runoff forced by
strengthening of the west-to-east Northern Hemisphere atmospheric circulation corre-
sponding to a strengthening of the Arctic Oscillation index. These findings are confirmed in
recent results presented by McPhee (
2013
) and Koldunov et al. (
2013
). In addition, the
regional sea level jointly obtained from tide gauges and ERS-1, 2 and Envisat altimeter
satellites together with the gravity field and ocean dynamic topography observations from
GRACE and GOCE have also recently allowed new innovative studies of the climate-
critical mass changes and freshwater flux variations in the high latitude and Arctic Ocean
(e.g., Cheng et al.
2013
; Prandi et al.
2012
; Henry et al.
2012
; Knudsen et al.
2011
).
In this paper, a new GOCE-based geoid and mean dynamic topography (MDT) for the
high latitude and Arctic Ocean is obtained, assessed and compared to independent steric
height observations and state-of-the-art MDTs. Furthermore, comparisons of surface
velocity and transport in the Nordic Seas, based on the combination of GOCE gradiometer
gravity estimates and in situ hydrographic data, are done with estimates from several
forced coupled sea ice-ocean models, ocean surface drifter data and direct measurements.
The new findings and results are presented according to the ocean dynamic topography in
Sect.
2
, ocean surface circulation in Sect.
3
and volume transport in Sect.
4
. A summary
follows in Sect.
5
.
