International Polar Year 2007–2008 - WMO

significant than deposition of aerosols as a source of
iron to this polar region during autumn. Furthermore,
the iron distribution indicates the importance of
bottom sediments and hydrothermalism as sources
of iron to the deep Southern Ocean (Tagliabue et al.,
2010), sources that have been neglected in previous
biogeochemical models for the region. Distributions
of total dissolvable iron (TDFe), dissolved iron (DFe)
and soluble iron (SFe) were investigated during the
BONUS-GoodHope cruise in the Atlantic sector of the
Southern Ocean (34°S/17°E, 57°S/0°E) along a transect
from the subtropical domain to the Weddell Sea Gyre,
in February-March 2008. The highest concentrations
of DFe and TDFe were observed in the sub-tropical
domain, where continental margins and dust input
might be the main Fe sources. Complexation with
ligands from biological and continental origin could
explain the distributions of SFe and CFe along the
transect (Chever et al., submitted).
The first measurements of methylmercury in the
Southern Ocean were made during IPY, showing
high concentrations and an increase in the ratio
of methylmercury to apparent oxygen utilization
in Antarctic waters (Cossa et al., submitted). The
distribution can be explained by the co-location in
Antarctic waters of a large atmospheric source of
mercury (through mercury depletion events mediated
by halogens released during sea ice formation),
bacterial decomposition of organic matter produced
by intense phytoplankton blooms and upwelling of
methylmercury-enriched deep water. These results
have improved our understanding of the global
mercury cycle, confirmed evidence of open ocean
methylation and helped explain the elevated mercury
levels observed in Antarctic biota.
IPY experiments in the Australasian region revealed
that subantarctic phytoplankton blooms during
summer were driven by both seasonal iron supply
from southward advection of subtropical waters and
by wind-blown dust deposition, resulting in a strong
decoupling of iron and nutrient cycles (Bowie et al.,
2009). These observations have important longerterm
climatic implications since the frequency and
scale of dust emissions and the poleward extension
of western boundary currents are both predicted to
increase in the future, resulting in a greater influence
of subtropical water on the subantarctic zone.
The origin of the iron in the ocean can be derived
by correlating properties of related trace metals such
as aluminium and manganese. Dissolved aluminium in
the surface waters is a tracer of aeolian dust and dissolved
manganese can help to trace iron input from
the bottom. On the Greenwich meridian the near surface
concentration of aluminium is low (Fig. 2.3-8 top),
whereas manganese displays a maximum over the
mid-ocean ridge (Fig. 2.3-8 bottom) correlating with
dissolved iron (not shown) suggesting an iron input
from hydrothermal activity (Middag et al., 2010a,b).
A comprehensive examination of the distribution,
speciation, cycling and role of iron in fuelling sea icebased
and pelagic algal communities showed that
primary productivity in seasonally ice-covered waters
around Antarctica is primarily driven by temporal
variations in iron supply (seasonal and inter-annual,
driven by sea ice formation and melting processes)
rather than large-scale spatial forcing (van der Merwe
et al., 2009), with strong vertical iron resupply during
winter, rapid release from sea ice and uptake during
spring, and substantial depletion during summer
(Lannuzel et al., 2010).
Marine biology, ecology and biodiversity
Several major programs, CAML, EBA, ICED, MEOP
and SCAR-MarBIN, numerous individual IPY projects,
PAME, AMES and certain components of PANDA,
focused on the broad issue of marine biology, ecology
and biodiversity in the Southern Ocean. These
overarching programs included contributions from
numerous regional programs, such as DRAKEBIOSEAS
and ClicOPEN, which focussed on the effect of climate
change on coastal communities at the western
Antarctic Peninsula.
The objective of the SCAR project Census of
Antarctic Marine Life (CAML, see www.caml.aq) was
to determine the distribution and abundance of life
in the Southern Ocean around Antarctica, providing
a benchmark against which future change can be
assessed. The Arctic and the Antarctic Peninsula are
currently experiencing rapid rates of change (IPCC,
2007; Steig et al., 2009; Mayewski et al., 2009; Convey
et al., 2009). The uniquely adapted organisms of the
polar regions may be vulnerable to shifts in climate
and ocean circulation patterns. The major scientific
question for CAML is how the marine life around
s C I e n C e P r o g r a m 199