The western Antarctic Peninsula harbours a diverse benthic marine community where dense canopies of macroalgae can dominate the shallow subtidal zone (0–40 m or greater). In the lower portion of this range (below 25–35 m depending on topography), invertebrates such as sponges and echinoderms can be found in greater abundance due to reduced competition for space from the algal species. Dendrilla antarctica (previously Dendrilla membranosa) is a common demosponge that thrives in both communities and is known for producing diterpene secondary metabolites as a defence against sympatric sea star and amphipod predators. Omnivorous mesograzers such as amphipods inhabit both communities; however, they are in greatest abundance within the macroalgal canopy. Due to the differences between habitats, it was hypothesized that specific amphipod species not susceptible to the defensive metabolites of D. antarctica would take refuge from predators in the chemically defended sponge. Analysis of the metabolome and amphipod communities from sponges in both habitats found correlations of metabolic profile to both abundance and habitat. These studies serve to inform our understanding of the complex ecosystem of the Antarctic benthos that stands to be dramatically altered by the rapidly changing climate in the years to come.

The western Antarctic Peninsula is facing rapid environmental changes and many recent publications stress the need to gain new knowledge regarding ecosystems responses to these changes. In the framework of the Belgica 121 expedition, we tested the use of a nimble vessel with a moderate environmental footprint as an approach to tackle the urgent needs of the Southern Ocean research community in terms of knowledge regarding the levels of marine biodiversity in shallow areas and the potential impacts of retreating glaciers on this biodiversity in combination with increasing tourism pressure. We discuss the strengths and drawbacks of using a 75’ (23 m) sailboat in this research framework, as well as its sampling and environmental efficiency. We propose that the scientific community considers this approach to 1) fill specific knowledge gaps and 2) improve the general coherence of the research objectives of the Antarctic scientific community in terms of biodiversity conservation and the image that such conservation conveys to the general public.

Recent rapid retreat of glacial front lines and the loss of land ice along the Antarctic margins may play an important role in exporting suspended particulate matter (SPM) potentially rich in bioavailable (defined as ascorbate leachable) iron (FeA) to coastal areas of the Southern Ocean. Sediment ablation is an additional source of iron for this high-nutrient low-chlorophyll region. In Potter Cove, King George Island, meltwater streams discharge up to 18 000 mg l-1 (average 283 mg l-1) of slightly weathered, finely ground bedrock particles into coastal waters during the summer. Approximately 15% of this SPM is exported within a low-salinity surface plume into Bransfield Strait. Based on our data, an estimated 12 mg m-2 yr-1 of FeA is exported from the South Shetland Island land surface (ice-free and subglacial areas) to the surrounding coastal waters. Extrapolated to an area of 2.5x104 km2, this FeA input is comparable to the contribution from icebergs and c. 240-fold higher than aeolian input via dust. An observed rise in local sediment accumulation rates suggests that glacial erosion has been increasing over recent decades and that (sub-)glacially derived SPM is becoming more important as a source of iron to the Southern Ocean.

During RV Polarstern cruise ANT-XXIII/4 in 2006, a gravity core (PS 69/335-2) and a giant box core (PS 69/335-1) were retrieved from Maxwell Bay off King George Island (KGI). Comprehensive geochemical (bulk parameters, quantitative XRF, Inductively Coupled Plasma Mass Spectrometry) and radiometric dating analyses (14C, 210Pb) were performed on both cores. A comparison with geochemical data from local bedrock demonstrates a mostly detrital origin for the sediments, but also points to an overprint from changing bioproductivity in the overlying water column in addition to early diagenetic processes. Furthermore, ten tephra layers that were most probably derived from volcanic activity on Deception Island were identified. Variations in the vertical distribution of selected elements in Maxwell Bay sediments further indicate a shift in source rock provenance as a result of changing glacier extents during the past c. 1750 years that may be linked to the Little Ice Age and the Medieval Warm Period. Whereas no evidence for a significant increase in chemical weathering rates was found, 210Pb data revealed that mass accumulation rates in Maxwell Bay have almost tripled since the 1940s (0.66 g cm-2 yr-1 in ad 2006), which is probably linked to rapid glacier retreat in this region due to recent warming.

Energy transfer in microbial food webs is partly quantified by the relationship between bacterial and algal biomass. Tight spatial relationships suggest active bacterial assimilation of dissolved photosynthate in temperate marine and fresh waters. However, studies in the Antarctic suggest that bacterial biomass generation from algal-derived dissolved organic matter is highly variable across seasons and habitats. Regression analysis was used to measure how bacteria covaried with algae in sea ice and water column habitats at three sites around Antarctica. Bacteria and algae were positively related in sea ice of the Weddell Sea during early winter 1992 (r2 = 0.16, slope = 0.24) and across sea ice and upper water column habitats of the Ross Sea during summer 1999 (r2 = 0.52, slope = 0.50). Conversely, bacteria and algae exhibited no discernible relationship in the water column and first year ice habitats of the Western Antarctic Peninsula region in winter 2001 (r2 = 0.003, slope = −0.04). Low algal production and residual biomass probably limited bacterial production and facilitated bacteria-algae uncoupling in winter sea ice of the Western Antarctic Peninsula. Winter sea ice algal biomass was probably limited by a relatively late date of initial ice formation, reduced multi-year ice coverage, and a lack of radiant energy in the winter ice pack.