Recurrent seascape units identify key ecological processes along the western Antarctic Peninsula

Abstract

The western Antarctic Peninsula (WAP) is a bellwether of global climate change and natural laboratory for identifying interactions between climate and ecosystems. The Palmer Long-Term Ecological Research (LTER) project has collected data on key ecological and environmental processes along the WAP since 1993. To better understand how key ecological parameters are changing across space and time, we developed a novel seascape classification approach based on in situ temperature, salinity, chlorophyll a, nitrate + nitrite, phosphate, and silicate. We anticipate that this approach will be broadly applicable to other geographical areas. Through the application of self-organizing maps (SOMs), we identified eight recurrent seascape units (SUs) in these data. These SUs have strong fidelity to known regional water masses but with an additional layer of biogeochemical detail, allowing us to identify multiple distinct nutrient profiles in several water masses. To identify the temporal and spatial distribution of these SUs, we mapped them across the Palmer LTER sampling grid via objective mapping of the original parameters. Analysis of the abundance and distribution of SUs since 1993 suggests two year types characterized by the partitioning of chlorophyll a into SUs with different spatial characteristics. By developing generalized linear models for correlated, time-lagged external drivers, we conclude that early spring sea ice conditions exert a strong influence on the distribution of chlorophyll a and nutrients along the WAP, but not necessarily the total chlorophyll a inventory. Because the distribution and density of phytoplankton biomass can have an impact on biomass transfer to the upper trophic levels, these results highlight anticipated links between the WAP marine ecosystem and climate.

Ecosystem Service Supply in the Antarctic Peninsula Region: Evaluating an Expert-Based Assessment Approach and a Novel Seascape Data Model

“…The Palmer LTER regional survey grid (Waters and Smith, 1992;Pal LTER, 2016) is located on the western side of the AP and spans from the continental slope (depth > 3,000 m) to coastal waters (Figure 1). For this part of the AP study area, Bowman et al (2018) had developed a novel approach to classify seascapes. We employed the derived SUs in this study as an alternative data model to define SPUs for a subset of the Palmer LTER regional survey grid area (see Figure 1), and to test their applicability to the matrix method.…”

“…First, we considered a classical approach that defines SPUs on the basis of geospatial land and ice cover, and relief data; this was done for the entire AP study area. Second, we considered a novel classification of recurrent SUs which builds on physico-chemical parameters; this dataset had been developed by Bowman et al (2018) for a subset of the Palmer LTER regional survey grid (see Figure 1).…”

“…All of these SPUs present fixed units, but they may change slowly with time due to processes such as sea level rise or the melting of ice shelves and glaciers. For the Palmer LTER study area subset, a novel data model describing recurrent SUs as developed by Bowman et al (2018) was employed to explore an alternative concept of SPU definition for coastal and open ocean waters. Similar to terrestrial environments, marine areas can be described as a three-dimensional mosaic of different habitats or "seascapes" with distinct characteristics reflecting their physical, chemical, and biological nature and occurrence in space and time (Hidalgo et al, 2016;Kavanaugh et al, 2016;Manderson, 2016).…”

“…These favorable conditions are provided by a complex interplay between sea ice, bathymetry, and ocean circulation. Winter sea ice cover allows the water column to stratify after fall deep-mixing events, setting the stage for the spring phytoplankton bloom (Bowman et al, 2018), while submarine canyons transiting the shelf enable the topographically induced upwelling of nutrient-rich Upper Circumpolar Deep Water (UCDW) (Kavanaugh et al, 2015). This careful balance of conditions is prone to variations in sea ice cover and the strength of the westerly winds that drive surface ocean circulation patterns south of the Polar Front.…”

“…Here we leverage expertise from the Palmer Long Term Ecological Research (LTER) project, an interdisciplinary science project initiated in 1993, to estimate ES along the AP employing an expert-based assessment approach, the matrix method. We employ and compare a novel data model to describe marine SPUs from physico-chemically defined seascape units (SUs) (Bowman et al, 2018) against conventional SPUs, and introduce the application of objectively defined seascape data with the matrix method as a potentially transformative tool for ES valuation in Antarctica, and in marine environments more broadly.…”