What is PESAS?

The Paleoecology of Subarctic Seas working group (PESAS) is a regional community of scholars dedicated to the interdisciplinary study of coupled human-natural systems in the past as they have played out in the maritime regions of the high latitude northern hemisphere. Formed as a working groups within the Ecosystem Studies of Subarctic and Arctic Seas (ESSAS: https://essas.arc.hokudai.ac.jp/) regional program, PESAS provides a context for the sharing and integration of paleo-research on atmospheric, oceanographic, marine-ecological, and human histories over time scales of millennia to centuries. PESAS embraces research spanning the last 20,000 years, from the last glacial maximum and deglacial period, when people first settled some high-latitude maritime regions (e.g., Fitzhugh Reference Fitzhugh, Brown, Misarti, Takase and Tremayne2022), to recent centuries, when massive commercial fisheries became ubiquitous and extraction came to threaten marine ecosystems globally (Pauly et al., Reference Pauly, Christensen, Dalsgaard, Froese and Torres1998; Jackson et al., Reference Jackson, Kirby, Berger, Bjorndal, Botsford, Bourque, Bradbury, Cooke, Erlandson, Estes and Hughes2001, Holm et al., Reference Holm, Ludlow, Scherer, Travis, Allaire, Brito and & Nicholls2019 [this issue], West et al., Reference West, Etnier, Barbeaux, Partlow and Orlov2020 [this issue]).

PESAS formed in 2014 and has met nearly annually at ESSAS meetings and in other venues, to bring together natural scientists, social scientists and environmental historians working around the North Pacific and North Atlantic margins. Participants in these meetings and workshops seek to explore the interconnected relationships between climate, oceanography and human history through interdisciplinary integration and inter-regional comparisons. PESAS originally targeted subarctic coastal and marine regions of the North Pacific and North Atlantic oceans, and the contributions in this issue predominantly share that orientation. The PESAS mandate has since expanded—along with the mission of ESSAS—to include the Arctic Ocean and inland waters of the Canadian Archipelago. In 2018, PESAS also joined forces with the Oceans Past Initiative (OPI: https://oceanspast.org/), a global network of paleoecologists, archaeologist and environmental historians exploring the legacies of human histories on the current conditions and future sustainability of ocean-human health and sustainability.

PESAS was initially brought together with the assistance of an NSF workshop grant supporting travel to Copenhagen for the Ecosystem Studies of Subarctic Seas (ESSAS) fisheries ecology annual science meeting in April 2014. ESSAS is a regional group, currently organized under the umbrella of the global Integrated Marine Biosphere Research program (IMBeR), itself a thematic research organization under the auspices of the Future Earth program. PESAS was admitted into ESSAS as an official working group to bring a “paleo-perspective” to ESSAS and to take advantage of the process-oriented interdisciplinary scholarship being conducted on modern subarctic marine ecosystems by ESSAS oceanographers, ecologists, economists, managers and modelers.

PESAS has held workshops, panels and talks as part of each subsequent ESSAS annual and open science meeting as well as at conventions of the American Association for the Advancement of Science (AAAS), International Union for Quaternary Research (INQUA), Oceans Past Initiative (OPI), and others. These activities were organized to identify, explore and try to answer “big questions” about the human/eco-dynamics of past high latitude marine systems and the implications of past human-environmental interactions for current and future resilience and adaptation. Research addressed at PESAS meetings has spanned almost 20,000 years and engaged the coupled dynamics of human and environment relationships from millennia to decadal time scales. PESAS members are interested in studying these relationships to examine the contexts of relational change and the dynamic capacities of natural and cultural systems to sustain themselves through changes in critical inputs. These kinds of insights are essential if we hope to better understand our own human vulnerability (as individuals, societies, and caretakers of valued natural systems). Put otherwise, PESAS seeks to synthesize what is known about past high-latitude ocean ecosystems (including human communities as actors within those systems), and then to identify questions and future research directions that might help address pressing issues related to the effects of global change on our oceans, and the role of our oceans in regional and global change—past, present and future.

This Special Issue

This issue represents the first integrated product of the PESAS working group. Here, PESAS participants cover a broad range of research including paleoclimate, paleoceanography, paleoecology, zooarchaeology, archaeology, history, fisheries biology and management. Each of the eleven manuscripts was born from PESAS participants’ engagement in efforts to explore long-term linkages between physical, biological and human dynamics. Contributed research showcases the efforts of scholars in both the Atlantic and Pacific worlds and how they intersect and diverge. Some papers are linked through methodology (many utilize isogeochemical techniques) or taxonomic foci (e.g., Pacific and Atlantic walruses or Pacific and Atlantic cod), while others are related through discussions of ecological processes such as bottom-up or top-down mechanisms linking climate, biochemical, ecological, sociopolitical and economic relationships. All contributions are underpinned by paleoceanographic records and radiocarbon chronologies, and every one of these themes is addressed in studies of either or both of these large, suboceanic basins.

Four taxa, in two pairs, Atlantic walrus (Odobenus rosmarus rosmarus), Pacific walrus (Odobenus rosmarus divergens), Pacific cod (Gadus macrocephalus) and Atlantic cod (Gadus morhua) receive particular attention in this collection. Biogeographically isolated in each ocean basin, but with shared evolutionary histories, respectively, walrus and cod were, and in some cases still are, highly utilized resources in both the subsistence and commercial realms of the subarctic North Atlantic and North Pacific. Xénia Keighley and colleagues (Reference Keighley, Olsen and Jordan2019) frame a series of vital questions about human-walrus interactions through time in the North Atlantic based on a deep literature review of Atlantic walrus research from aDNA to faunal analyses. Despite in-depth modern biological and ecological research on walruses, the authors highlight how poorly we understand the role of past human hunting (at both the subsistence and commercial levels) and it's impacts on our current “baseline” for walrus populations. Keighly et al. propose methods to create “a shared point of reference for the humanities and natural and social sciences to understand human-walrus interactions through time.”

Casey Clark and collaborators (Reference Clark, Horstmann, de Vernal, Jensen and Misarti2019), utilize some of those methods (sea ice reconstruction and stable isotope analyses) to examine the changing role of sea ice and climate on Pacific walrus diets over the last 4000 years. They find, among other conclusions, that despite notable changes in diet through time, sea ice is not a predominant factor in those changes. This contrasts with current assumptions in the biological community. Although changes in diet are only one factor in potential impacts to walruses as we face dramatic losses in sea ice in regions of prime habitat today, evidence that walruses’ diet has changed in discernable ways while the species remains resilient is an important finding for co-management groups in Alaska as they evaluate future policies.

Pacific and Atlantic cod provide another productive pairing. Catherine West et al. (Reference West, Etnier, Barbeaux, Partlow and Orlov2020) compare harvested Pacific cod size data from 6000 years of archaeological sites and modern commercial long-line fisheries around the North Pacific Rim (Kuril Islands to Southeast Alaska). Finding few significant differences between pre-commercial and commercial catch records, they argue that neither pre-industrial harvests nor long-term climate change had measurable effects on fish population structures (i.e., no evidence of “fishing down the food chain” with possible exception of sites in the Western Gulf of Alaska where commercial fishing had its earliest start). These are important findings as they suggest that taxa like Pacific cod were resilient to both top-down and bottom-up impacts through the last 6000 years, potentially tied to the stock's tendency to migrate to different areas and water depths on the continental shelf dependant on preferred temperatures. That same tendency that made cod stocks resilient created problems for human harvesters who periodically lost access to the fish when they moved to deeper or more distant waters (Betts et al., 2009).

The Atlantic cod fishery has a longer history of intensive commercial exploitation, dating back to the 14^th and 15^th centuries, a history that eventually contributed to more vulnerable stocks. George Hambrecht and company (Reference Hambrecht, Feeley, Smiarowski, Hicks, Harrison, Brewington, Cesario and Gibbons2019) synthesize the last 1000 years of zooarchaeological data on Atlantic cod fishing in Iceland. This interval starts in the era of medieval Norse farming and locally-based fishing and was followed mid-millennia by the emergence of intensive commodities-based fisheries for export to European markets tied to the dawn of the ‘Modern Era’ in European history. This paper considers the linkages between zooarchaeological trends and proxy climatic data in this time frame and accounts for those patterns with reference to sociopolitical, economic and technological change documented in historical records. Ragnar Edvarsson et al. (Reference Edvardsson, Patterson, Bárðarson, Timsic and Ólafsdóttir2019) take a complementary approach to the Iceland ‘cod story’, employing biogeochemistry, historical documents and archaeology to track changes in cod fishing in Iceland from the onset of the Little Ice Age to the mid-1800s. Significantly, evidence reported in both papers reveal changes in Icelandic fisheries and fish populations at the time of a modernization of fishing technology in Iceland during the 1800s.

Changes in Icelandic and other North Atlantic fisheries are part of the larger pattern that Poul Holm and colleagues (Reference Holm, Ludlow, Scherer, Travis, Allaire, Brito and & Nicholls2019) term “The North Atlantic ‘Fish Revolution’.” In their prospective ‘Forum’ article, they ask three basic but important questions concerning to the relationship between economics, human population growth and migration across the North Atlantic (from Europe): what were the environmental parameters that set the stage for the expansion of European North Atlantic fisheries; how did the ‘Fish Revolution’ affect global economic and social history; and how did it change fishing communities themselves? Their paper lays out a strong direction for future research that integrates the human sociopolitical and economic forces and the changing marine environments over recent centuries.

The aforementioned papers focus on stocks of marine mammals and fish important to human economies and cultures in the subarctic regions of both oceans. Humans also have population-level characteristics that are influenced by the availability of quality food and other necessities. As such, human populations are dynamically coupled to and dependent on the ecosystems that support their well-being. Human population dynamics of subsistence-based communities, and the extent to which they are influenced by environmental and other changes, are explored in two included articles. These papers take advantage of new techniques to assimilate large numbers of radiocarbon dates to generate proxy estimates of human population change through time. In each case, the authors of these papers compare paleodemographic trends between regions and against evidence of environmental and factors that could help explain fluctuating trends. Erlend Jørgensen et al. (Reference Jørgensen, Pesonen and Tallavaara2020) take this approach to compare archaeological population histories on Norway's Arctic coast and northern Finland's Gulf of Bothnia coast. They attribute synchronous population growth and decline between 6500 and 4500 cal yr BP in the Scandinavian series to parallel cultural and demographic responses to changes in the marine productivity of the respective nearshore environments. Ben Fitzhugh and colleagues (Reference Fitzhugh, Brown, Misarti, Takase and Tremayne2022) take on a larger scale problem in seeking to document and interpret population proxy models from fourteen distinct regions around Alaska, Hokkaido and the Kuril Islands. Their paper seeks to evaluate a previously described inverse correlation in population trends between southern Alaskan and the Kurils (Fitzhugh et al., 2020) and to explore the possibility that those trends might be driven, in part, by an oscillating ecological regime shift tied to millennial-scale fluctuations in the strength and location of the Aleutian Low storm track, with bottom-up effects. In the process, they tackle a range of issues in archaeological paleodemography and introduce a new method for statistically comparing time series.

A prerequisite to all of these papers is the ability to place paleo-proxy data into reasonably accurate chronological context. In this volume, Khasanov et al. (Reference Khasanov, Fitzhugh, Nakamura, Okuno, Hatfield, Krylovich and Savinetsky2020) present new, marine reservoir corrections for radiocarbon dates from Chukotka, the Commander Islands and Shemya Island in the western Aleutians. They put that information into the larger context of existing information from the greater North Pacific region providing the most up-to-date picture of variation in the persistence of old carbon in North Pacific waters with significance for paleoceanographic reconstructions and any efforts to use marine samples for radiocarbon dating. Limited understanding of these dynamics has hampered North Pacific maritime archaeological and paleo-ecological research at the center of the PESAS mission.

All of the research collated in this volume, to one degree or another, seeks to include evidence of past climate dynamics as they may have influenced marine ecosystem structure and change with implications for human consumers of ecosystem services. Camille Brice and colleagues (Reference Brice, De Vernal, Ivanova, Van Bellen and Van Nieuwenhove2020) report on postglacial changes in dinocyst assemblages from a core in the northwestern Barents Sea just east of Svalbard. This area is rapidly becoming a region of interest for fisheries ecologists and commercial operations as a warming climate shifts prime fish habitat north. In that context, Brice et al.'s paper provides a particularly interesting look at the dynamic history of the region's ecology. Despite hemispherically warm summers from the early to mid-Holocene, they find a lack of stable climate conditions and low productivity throughout most of the Holocene. Harsh glacial-like conditions existed in the Barents Sea until at least 8700 cal yr BP, when proxy data show the first shift towards more interglacial sea surface conditions. This included increased sea surface temperatures and productivity and a decrease in sea ice cover. However, large scale change variations in conditions appear to persist throughout the next few thousand years. The only exception to this is from 4000 to 2000 cal yr BP. During that 2000 year time frame primary productivity was high and coincided with a potential influx of warmer North Atlantic surface waters and optimal salinity conditions. Although not direct evidence, this time period does coincide with the archaeological hypothesis of the first human habitation of Svalbard Island. Overall, Brice et al.'s 15,000 year record makes the case that conditions in the Barents Sea Arctic region have rarely supported robust marine ecosystems capable of sustaining human habitation this far north until more recent times.

On the Pacific side and a bit further south, the Aleutian Low (AL) climate system that dominates North Pacific storminess strongly conditions the intensity and spatial distribution of nutrient supply, primary productivity, and ecosystem food-web dynamics today. Nagashima et al. (Reference Nagashima, Addison, Irino, Omori, Yoshimura and Harada2021) seek to document multi-centennial to millennial-scale changes in the AL over the last 7500 years. Having previously documented millennial-scale variation in the Holocene Western Asian Jet Stream from proxy analyses in East Asia (Nagashima et al. 2007, 2013), the authors here compile seven paleotemperature proxy series (δ¹⁸O) from western North America. In undertaking research to help understand these key drivers for paleo- and neo-ecological studies, this paper contributes to papers in this volume, especially that of Fitzhugh et al., but also, by analogy, for the work of Holm and colleagues in the North Atlantic.

Nagashima and co-authors conceived of and developed their research, in part, in response to early PESAS working group discussions seeking plausible explanations for the perceived inverse correlations in proxy human population trends between the northeast and northwest Pacific that are reported most fully in Fitzhugh et al.'s paper (this issue). This is just one example of how this issue showcases the strengths of large, interdisciplinary working groups probing the links between climate, ecology/biology, and human socioeconomic systems. While this particular example features a hypothesis of environmentally influenced ecological and human demographic variability, as Hambrecht et al., Holm et al., Edvardsson et al. and Fitzhugh et al. discuss, humans both alter and are affected by the landscapes they inhabit. Social, cultural and economic dynamics also play important roles in the trajectory of the historical/paleo-ecological and human perspective. PESAS, as a group, has been researching for nearly a decade at this point.

In 2016 IMBeR laid out three grand challenges: Grand Challenge I: Understanding and quantifying the state and variability of marine ecosystems; Grand Challenge II: Improving scenarios, predictions and projections of future ocean-human systems at multiple scales; and Grand Challenge III: Improving and achieving sustainable ocean governance (Hoffman et al., Reference Hofmann2016). PESAS scholars contend that in order to meet those challenges we must begin to understand the past interactions and dynamics between humans and other species in our marine environments, the ecological processes that entangle them, and the physical processes that frame them. We believe that this Quaternary Research volume contributes greatly towards this goal.