• Energy Research

The west Antarctic Peninsula (WAP) region has undergone significant changes in temperature and seasonal ice dynamics since the mid-twentieth century, with strong impacts on the regional ecosystem, ocean chemistry and hydrographic properties. Changes to these long-term trends of warming and sea ice decline have been observed in the 21st century, but their consequences for ocean physics, chemistry and the ecology of the high-productivity shelf ecosystem are yet to be fully established. The WAP shelf is important for regional krill stocks and higher trophic levels, whilst the degree of variability and change in the physical environment and documented biological and biogeochemical responses make this a model system for how climate and sea ice changes might restructure high-latitude ecosystems. Although this region is arguably the best-measured and best-understood shelf region around Antarctica, significant gaps remain in spatial and temporal data capable of resolving the atmosphere-ice-ocean-ecosystem feedbacks that control the dynamics and evolution of this complex polar system. Here we summarise the current state of knowledge regarding the key mechanisms and interactions regulating the physical, biogeochemical and biological processes at work, the ways in which the shelf environment is changing, and the ecosystem response to the changes underway. We outline the overarching cross-disciplinary priorities for future research, as well as the most important discipline-specific objectives. Underpinning these priorities and objectives is the need to better define the causes, magnitude and timescales of variability and change at all levels of the system. A combination of traditional and innovative approaches will be critical to addressing these priorities and developing a co-ordinated observing system for the WAP shelf, which is required to detect and elucidate change into the future.

The Western Antarctic Peninsula (WAP) is a highly productive marine environment that is undergoing rapid change, with consequences for productivity and total ecosystem carbon cycling. We present continuous underway O2/Ar estimates of net community production (NCPO2Ar) in austral summer 2012, 2013 and 2014 at sub-kilometer horizontal resolution within the Palmer Long-Term Ecological Research (Pal-LTER) grid region of the WAP. Substantial spatial variability is observed with NCPO2Ar ranging from 0 to 790 mmol O2 m−2 d−1 and considerable interannual variability with mean values in the grid region of 54.4±48.5, 44.6±40.5, and 85.6±75.9 mmol O2 m−2 d−1 in 2012, 2013 and 2014 respectively. Based on a strong correlation (r2=0.83) between residence time integrated NCPO2Ar and NCPDIC derived from seasonal DIC drawdown, we find the observed NCPO2Ar spatial and interannual variability to be consistent with the December–January NCPDIC magnitude. Seeking to explain the mechanistic drivers of NCP in the WAP, we observe a linear relationship between NCPO2Ar and meteoric water content derived from δ18O and salinity. This correlation may be due to Fe supply from glacial melt and/or strengthening of stratification and relief of light limitation. Elevated surface Fe availability, as indicated by Fv/Fm and measurements of surface water dissolved Fe and Mn (a rough proxy for recent potential Fe availability), and shallower, more stable mixed layers are present where meteoric water and/or sea ice melt is high near the coast. Light limitation is evident in the WAP when mixed layer depths are greater than ~40 m. Additionally we document hotspots of NCP associated with submarine canyons along the WAP. While it is difficult to predict how the physical-biological system might evolve under changing climatic conditions, it is evident that NCP, and potentially carbon flux out of the mixed layer, along the WAP will be sensitive to shifts in meltwater input and timing.

SummaryAn 8‐year time‐series in the Western Antarctic Peninsula (WAP) with an approximately weekly sampling frequency was used to elucidate changes in virioplankton abundance and their drivers in this climatically sensitive region. Virioplankton abundances at the coastal WAP show a pronounced seasonal cycle with interannual variability in the timing and magnitude of the summer maxima. Bacterioplankton abundance is the most influential driving factor of the virioplankton, and exhibit closely coupled dynamics. Sea ice cover and duration predetermine levels of phytoplankton stock and thus, influence virioplankton by dictating the substrates available to the bacterioplankton. However, variations in the composition of the phytoplankton community and particularly the prominence of Diatoms inferred from silicate drawdown, drive interannual differences in the magnitude of the virioplankton bloom; likely again mediated through changes in the bacterioplankton. Their findings suggest that future warming within the WAP will cause changes in sea ice that will influence viruses and their microbial hosts through changes in the timing, magnitude and composition of the phytoplankton bloom. Thus, the flow of matter and energy through the viral shunt may be decreased with consequences for the Antarctic food web and element cycling.

The Southern Ocean is fundamental to the operation of the Earth system. It is the central connection among the major ocean basins and between the upper and lower layers of the global ocean circulation. It influences global climate and planetary‐scale biogeochemical cycles, because the Southern Ocean accounts for half of the annual ocean uptake of anthropogenic carbon from the atmosphere [Rintoul et al., 2001; Le Quéré et al., 2007; Meredith et al., 2012]. The Southern Ocean also supplies nutrients that fertilize the majority of global ocean biological productivity north of 30°S [Sarmiento et al., 2004].

Analysis of satellite altimeter data reveals anomalously high Eddy Kinetic Energy (EKE) in the Antarctic Circumpolar Current (ACC) during the period 2000–2002. Around 2–3 years earlier (1998), the circumpolar eastward wind stress (as quantified by the Southern Annular Mode; SAM) showed a significant positive peak, and we have shown previously that the ACC peaked around 1998 in response. An eddy‐resolving ocean model is used to investigate the delay between wind forcing and the eddy response, and demonstrates that the lag is due to the time taken to influence the deep circulation of the ACC. Winds over the Southern Ocean have shown a strong climatic increase over the past few decades. If this increase in winds is also reflected as an increase in eddy activity (as our analysis suggests it might), then the increased poleward heat flux may have played a significant role in the observed warming of the Southern Ocean.