Earlier highlights: 1991

Intellectual Evolution and Context of the Palmer LTER

Although our initial concept of the importance of the effects of seasonal sea ice dynamics on the vitality of all levels of the pelagic ecosystem remains at the core of our research, we have a growing understanding of the complexities of the coupled atmosphere-ocean-sea ice-biota interactions. Our first working hypotheses were relatively simplistic, and focused on the extent of pack ice in winter as the sea ice variable with the most impact. This paradigm underwent a shift as we recognized that timing and duration of sea ice also had an impact at various levels of the ecosystem, and that the various components of the ecosystem responded differently to the same factor. Initially we recognized that other physical factors, such as variations in oceanic circulation, would also affect biological processes. Recent analyses have shown both the pervasiveness of warmer Upper Circumpolar Deep Water on the shelf, and interannual variability in its horizontal extent, and a role for the UCDW suggested feedback with the atmosphere.

We also became increasing aware of tropical/high latitude teleconnections, e.g. the links between Antarctic waters in the south east Pacific (waters west of the Antarctic Peninsula) and ENSO conditions in the tropical Pacific. As the long-term data sets increased, and analyses of climate data began to show statistically significant warming trends and a trend toward later and later sea ice formation in the fall, and that the Adelie penguin population numbers were decreasing around Anvers I., we were faced with the challenge of detecting trends against a background of strong interannual variability, decadal scales of variability, regime shifts, and/or long term cycles. We had to think about possible ecological responses to climate change, and what kinds of data we need both to detect current responses and to predict responses in the future. Our working hypotheses began to incorporate ideas about non-linear responses to changing conditions, about how changes in timing of life cycles of predator and prey could create “mismatches” in the need for and availability of food, and optimal habitats defined by different suites of conditions depending on the species investigated. Midway through this third granting period we find ourselves on the threshold of being able to detect and interrelate responses in the pelagic ecosystem west of the Antarctic Peninsula.

PAL Working Hypothesis I: 1991-1996

Our central hypothesis states that many significant biological processes in the Antarctic marine environment are strongly affected by physical factors, particularly the annual advance & retreat of pack ice & variations in ocean currents. Our conceptual model of the interaction between these physical processes & the components of the ecosystem is based on our present knowledge of interannual variability in the extent of pack ice & in the reproductive success of the species that dominate energy flow.

Ho: We hypothesize that interannual variation in the extent of pack ice affects the vitality of ice edge phytoplankton, & associated krill & seabird populations.

PAL Working Hypotheses II: 1996-2002

The PAL program remains focused on understanding the ecological role of sea ice with the primary object being to gain a general understanding of the physical & climatic controls on interannual sea ice variability, the effects of this variability on trophic interactions, & the biogeochemical consequences thereof (PAL Group, 1996; Smith et al., 1995c). Our observational & experimental programs reflect this primary research goal.

Ho: Neither the presence nor the extent of annual sea ice in the PAL study area influences ecosystem structure & dynamics.

PAL Working Hypotheses III: 2002-2008

The PAL LTER was established in 1990 within the framing hypothesis that the annual advance and retreat of sea ice is the major physical determinant of spatial and temporal changes in the structure and function of the Antarctic marine ecosystem. As the program matured, the core of PAL remained focused on the ecological role of sea ice, the physical and climatic controls on interannual sea ice variability, and on the effects of this variability on trophic interactions and biogeochemical processes. During PAL I and II, we detected a progressive poleward shift in the dominant climatic gradient along the West Antarctic Peninsula, observed a contemporary ENSO signal in sea ice patterns and primary productivity, and established a temperature trend we believe to be associated with observed global warming. In short, the atmospheric and marine fluids that support and sustain the ecosystems of the Palmer area are dynamic in time and space. At the inception of PAL, we established a measurement system along the West Antarctic Peninsula and in the environs of Palmer Station that permits us to study ecological dynamics as they vary in time and space in response to climate variation and climate change.

Ho(a): Climate migration associated with a warmer, more moist maritime regime that is becoming increasingly dominant along the north and central WAP region, is giving rise to ecosystem responses that take the form of changes in the abundance, distribution and community structure of all trophic levels.

Ho(b): Teleconnections to global scale atmospheric processes, with attendant quasi-periodic variability within this Antarctic marine ecosystem, modulates the observed longer term trends in climate and ecological processes.

PAL Working Hypothesis 2008-2014

The overall objectives of the Palmer, Antarctica LTER are:

1. To document and quantify the processes of climate and ecosystem change in the west Antarctic Peninsula continental shelf via nearshore land-based, offshore shipboard, unattended mooring, autonomous glider and satellite remote sensing observations;
2. To understand, through process measurements, manipulative experiments, comparative analysis against other marine ecosystems, data synthesis and modeling, the physical and ecological mechanisms of climate and ecosystem change; and
3. To predict/project the future course of ecosystem change in the west Antarctic Peninsula region. In order to investigate the mechanistic linkages between climate change and ecosystem response, we have broken the problem down into three inter-related components. Each of these forms the basis for a hypothesis and a group of coordinated observations, experimental process studies and modeling studies:

Hypothesis 1:

Regional warming, increased glacial meltwater inputs and sea ice decline associated with historical and on-going climate migration in the northern part of our study area have altered key trophic relationships, leading to changes in species distributions, increasing trophic mismatches and changes in habitat, food availability, ecosystem dynamics and biogeochemical cycling. The observations to address Hypothesis 1 include continuing the long-term historical PAL time-series near Palmer Station (nearshore ocean time-series and penguin ecology studies), offshore observations along the northern WAP (annual ship-based survey, sediment trap and expanded mooring network), and satellite remote sensing observations. New glider (small autonomous submarines equipped with sensors, Fig. 2.19) transects prior to, during, and after the ship-based survey will extend the seasonal observational coverage, and new bio-optical and trace metal measurements will probe in more detail aspects of phytoplankton physiology. In order to better characterize climate-trophic interactions, we will quantify the temporal and spatial correlations between observed physical variations and biogeochemical and ecological responses. Targeted process studies and local 1-D numerical simulations will be conducted to elucidate the mechanisms behind observed relationships.

Hypothesis 2:

Ecosystem conditions that prevailed prior to climate migration in the north will be found farther south along the Peninsula, forming a disturbance continuum along the WAP. We anticipate the climate migration trend will continue and reach the southern extreme of our study area within the next one to two decades, with our proposed studies providing a baseline for assessing future change. The ship-based annual regional survey and glider transects will be extended 200 km farther south to ocean areas ahead of the WAP climate migration, areas already covered by our on-going satellite data analysis. Comparative data analysis will be carried out on the northern and southern parts of the PAL survey grid, and process studies in both regions and the Palmer and Rothera time series will assess how climate gradients along WAP alter physical-ecological relationships. The field-based findings will be compared with 3-D regional ocean simulations along the Peninsula.

Hypothesis 3:

Deep cross-shelf troughs are focal regions with predictable elevated food resources for top-predators such as penguins, influencing their foraging ecology and the geographic distributions of breeding and wintering populations on timescales that are long relative to recent climate change. These relationships may already be disrupted in the northern part of our sampling grid. Mesoscale ship- and glider-based surveys and intensive process investigations will be used to identify better the physical and lower trophic level properties supporting the concentration of top predators above the troughs. Below we describe and further summarize our long-term observations, and follow with the proposed research for 2008-14. The proposed research has three major components: long term observations, including manned shipboard and remote, autonomous mooring and glider instrumentation; land- and ship-based process studies; and a new modeling component.