International Polar Year 2007–2008 - WMO

Fig.e 2.3-5. The
Weddell gyre
flow and in situ
temperature in 800
m depth derived
from the data of
206 ice-compatible
vertically profiling
floats between 1999
and 2010.
(Image: Fahrbach et al.,
submitted)
196
IPY 20 07–20 08
the Amery Ice Shelf have provided new insights into
melting and re-freezing processes in that sub-ice
shelf cavity (Craven et al., 2009). The Amery Ice Shelf
experiences rapid melt rates near its grounding line.
Most of this melt water re-freezes to the base of the
floating ice-shelf, forming a marine ice layer up to 200
m thick. This marine ice layer is highly permeable,
even at a distance of 100 m above the ice-shelf base.
The permeability of the marine ice layer suggests
that marine ice at the base of the ice-shelf may be
particularly vulnerable to changes in ocean properties.
Biogeochemistry
Most of the deep hydrographic sections occupied
by the CASO and SASSI programs also collected observations
of biogeochemical parameters, including
carbon and major- and micro-nutrients. In addition,
IPY-GEOTRACES contributed to 14 research cruises in
the oceans around Antarctica and the Arctic, as part
of the overall GEOTRACES study of the global marine
biogeochemical cycles of trace elements and their isotopes
(Measures et al., 2007).
A primary goal of the biogeochemistry program
during the IPY was to quantify the evolving inventory
of carbon dioxide in the Southern Ocean and to
understand how the physical and biological processes
responsible for ocean uptake and storage of CO 2 might
respond to climate change (Gloor et al., 2003; Hoppema,
2004; Takahashi et al., 2009). Another important issue
in the Southern Ocean is the vulnerability of the cold
surface waters to acidification. Here, the already low
concentration of carbonate ion is further reduced by
considerable uptake of anthropogenic CO 2 , possibly
leading to under-saturation of aragonite (a form of
CaCO 3 ) within the next decades (Orr et al., 2005; McNeil
and Matear, 2009). This in turn could have an impact
on CaCO 3 utilizing organisms by reducing the rate
of calcification. For example, pteropods, planktonic
snails that form shells from aragonite, are a key part
of the Southern Ocean food chain and may be at risk
as the Southern Ocean becomes progressively more
undersaturated in aragonite. Since not all organisms
act similarly and the distribution of organisms around
the circumpolar ocean is inhomogeneous, spatial
variability of ocean acidification and its impact on the
carbon cycle is expected. Measurements made during
IPY are being used to document the evolving inventory
of anthropogenic CO 2 and changes in ocean acidity.
The Southern Ocean is of particular interest to
GEOTRACES as iron limits primary productivity in
much of this region, and change in the delivery and
availability of iron will arguably be the single largest
forcing of Southern Ocean ecosystem productivity
and health in the next century, and thus is intrinsically
linked with changes in climate. Moreover, all living
organisms require trace elements (such as zinc, copper,
manganese and cobalt) for many functions including
as co-factors in enzymes thus co-limitation by such
elements in the Southern Ocean is likely under certain
environmental conditions (Morel and Price, 2003).
The scientific questions of primary interest to the
biogeochemical theme of Southern Ocean IPY in-