Reconstructing the “push” and “pull” of climate and its impacts on subsistence cultures using paleolimnology

Three peer-review indexes were used in the systematic mapping process: The Web of Science, PubMed, and Scopus. A string of search terms was generated to capture the research themes (Table 1); paleolimnology (paleolimnolog* OR palaeolimnolog*, and pal*limnolog* for search strings in Web of Science), human activity (settle*, migration*, subsist*, hunt*, human activity), climate (climat*), and response (stress*, adapt*). Duplicated results between the three indexes were removed. The searches were restricted to articles published between 1990 and 12 December 2020 when the search was completed, the consistency of decisions was reviewed 4 May 2021.

Inclusion criteria were determined in advance to validate the relevance and eligibility of search results; articles needed to be a primary source and needed to employ methods in paleolimnology. Articles using similar methods (such as paleoecology) were also included as these methodologies are often used in similar contexts. Articles that simply mentioned paleolimnology (or related methods) but did not include it as part of their methodology were not included. Articles were also required to relate to the subthemes of our review (human/subsistence activity, change, resilience, and vulnerability). Lastly, only articles published in English were included.

Articles were screened for relevance by means of their key words and the inclusion criteria. If the inclusion of paleolimnology or human/subsistence activity was not clear from the title or abstract, the full article was screened for key terms to determine the context. Articles that were found to fit the inclusion criteria and contained content relevant to paleolimnology and human/subsistence activity were included. Excluded articles, and reasons for exclusion, can be found in Supplementary Table S1. Initial search and data extraction was done by A. Covert, and consistency of decisions was checked by A. Medeiros.

The focus of this review was on how paleolimnology has been applied to study components of cultural activities pertaining to the subsistence economy of human populations in the late-Holocene and to map the range in which this research is covered in the literature. Meta-data were extracted from each article, including the year of publication, region of the study, notable features (themes), and the type of paleolimnological methodology employed. Once the articles from our key word search were narrowed down to those containing relevant information based on the inclusion criteria and selection process, a key word query with NVivo 12 PRO was performed. This extracted the top 100 words used in the articles to create a word cloud and identified primary themes represented in the literature. Relevant articles were analysed based on the study’s region of interest and year it was published. Some articles were relevant in more than one topic and were placed in multiple categories. Organizing the articles from our key word search based on content helped understand the context in which this area of research is available in the literature. While this is not a fully complete collection of articles that discuss this area of research, our results can help determine the range of themes that exist in the literature.

Climate change is a key factor in the spread of human populations across the globe, influencing environments that have predicated the migration of both species and peoples; migration is often an adaptive response to the push and pull factors of climate (Marr 2015). Large-scale changes in climate, such as significant warming and cooling periods, have been well researched through paleo-inferences of isotopic geochemistry and biological indicators in lacustrine sediments (Reheis 1999; Stefanova et al. 2003; Lozhkin and Anderson 2013; Adams et al. 2019). Twenty-six of the relevant 68 articles from our key word search studied large-scale changes in climate using geochemical and (or) biological indicators. Paleoenvironmental reconstruction of glacial change (Vegas-Vilarrúbia et al. 2013), southern oscillation (Rodysill et al. 2012), and hydrologic change (Magyari et al. 2009) all focus on large-scale changes associated with threshold shifts in biological indicators on a millennial scale. Paleolimnological studies have also supported revision of previous estimates of when large-scale changes occurred (Hoelzmann et al. 2001; Wolfe et al. 2012) as well as the amplitude and timing of ecosystem response (Wolfe et al. 1996). This has proven to be important for understanding the impact of climate forcing on biological change, as different biota have different thresholds at which they can tolerate change (Stefanova et al. 2003). Different taxa have differences in their optima and tolerance of environmental conditions in which they operate (Williamson et al. 2009).

While paleolimnological techniques can effectively reconstruct past environments, archaeological evidence is sometimes paired with these inferences to specify the presence of early human populations (Tudryn et al. 2013; Temoltzin-Loranca et al. 2018). Depending on the subsistence strategies employed, a region’s climate is known to influence whether the location is suitable for occupation (Liu et al. 2020), but direct evidence of human occupation is less apparent, especially in studies that deploy a single paleolimnological proxy. Paleolimnology has also been used to help confirm previous human occupation dates that were solely dated using archaeological data (Hoelzmann et al. 2001). While 18 of the 68 articles reviewed discussed human occupation, reconstructing human occupation was often not the main topic of focus. Human occupation was often discussed coincidently alongside other historical environmental information. For example, Schmidt et al. (2019) aimed to reconstruct the onset of stable freshwater conditions on Ruben Island, Japan, using multiproxy paleolimnological records, but they also discovered the appearance of the earliest settlement of sedentary hunter–gatherer populations (5000–4000 cal. Years BP).

The movement of early humans can largely be tied to environmental changes, especially when a region is no longer fit for occupation. For example, Inuit who rely on seal hunting are required to migrate further north when the sea ice is too thin to be able to safely hunt (Hadley et al. 2010). Twelve of the 68 articles from our key word search discussed human migration, often using paleolimnological techniques alongside archaeological evidence. For example, Hoelzmann et al. (2001) identified four settlement phases around a freshwater in the Eastern Sahara (Africa) during the Holocene epoch using a multi-proxy reconstruction approach of carbonates, oxygen and carbon isotopes, and diatoms, paired with the dates of stone tool remains. The chemical composition of the sediment core allowed for the inference of lake stages throughout history and provided context for why groups settled and abandoned the region in cycles. Indeed, several studies reconstructed the timing of human migration by inferring the timing of abandonment (Hoelzmann et al. 2001; Filippelli et al. 2010; Temoltzin-Loranca et al. 2018). For example, Filippelli et al. (2010) inferred abandonment of a once-continuous human occupation from the recovery of vegetation at the site.

A common theme in the field of paleolimnology is how anthropogenic stressors, such as the arrival of settlers or increased human development in lake basins, have led to ecological changes. Climate is often an integral component of understanding ecological stress, as climate factors can influence both the environment as well as human society (Todgham and Stillman 2013). We found that topics relating to how human society was influenced in relation to climate was more commonly covered in the literature than studies relating to where people lived (Table 2). Thirty-six articles from our key word search discussed how people lived and the impacts that they had on the environment. Indigenous cultures in the Canadian Arctic, in particular, have received large amounts of recent attention. This is not unexpected as climate change is significantly impacting the cultural continuity of the Indigenous Peoples of the Canadian Arctic (primarily Inuit) and the sustainability of their subsistence-sharing economy (Hadley et al. 2010; Michelutti et al. 2013). Paleolimnology can also identify impacts by subsistence/anthropogenic stressors in what were once thought to be pristine environments (Zawiska et al. 2013). For example, whaling camps by Thule Inuit impacted the water quality and ecology of high Arctic lakes as a result of constructing their settlements from nutrient-rich whale bones that over time leached nitrogen into freshwater bodies, altering their chemical composition (Douglas et al. 2004). The Thule society’s impact continues be evident despite these lakes having been abandoned centuries ago due to the legacy of nutrient enrichment that continues to leach into the water at these sites (Douglas et al. 2004).

Freshwater lakes are under threat globally from both natural and anthropogenic stress (Mills et al. 2017). As these systems are important for both cultural and subsistence practices, the environment (climate) can have a large influence on settlement and migration. Twenty-three articles from our key word search discussed the impact of both climate and anthropogenic stress on subsistence lifestyles. For example, lake-level is often associated with climate, which can influence agricultural practices as well as the presence of subsistence prey (Sedov et al. 2010). Paleolimnological inferences have documented examples of human society that transitioned from a low-impact nomadic lifestyle to a high-impact and overly consumptive sedentary lifestyle. These transitions frequently depend on the magnitude of the push or pull of climate on the ecosystem or ecological services that cultural activities depend on and the timing of climate events (Junginger and Trauth 2013). Water collection, hunting, fishing, gathering, and agriculture are all environment dependent, and adaptations to these practices are frequently tied to changes in climate, and more recently, technological advancements. While migration is a common response to environmental stress (Shaw 2016), adaptation or the transition to different subsistence practices was discussed in nine articles (Table 2). For example, Feeser et al. (2016) described the transition to animal husbandry inferred with the use of pollen during the Neolithic epoch (7000–4000 BP).

The context of how lakes have changed from their natural or predisturbed state provides key information for remediation projects and the creation of freshwater management plans. As such, paleolimnology can ultimately be considered an effective tool to achieve environmental sustainability (Saulnier-Talbot 2016). Environmental managers are better able to understand the trajectory of ecosystem change with a baseline context of the predisturbance state. This knowledge can then be applied to the management of ecosystem services that communities are reliant upon (Sullivan and Charles 1994). The use of paleolimnology to qualify freshwater sustainability was a common theme discussed in the literature, with 23 articles discussing the application of paleolimnological methods in the realm of water management. Popular themes identified focused on the influence of anthropogenic activities and how they have modified lake catchments (Magyari et al. 2009; Shaw Chraïbi et al. 2014), as well as changes in ecological status since the industrial revolution (Kirilova et al. 2009).

The reconstruction of lake trophic structure can be a determining factor for inferences on the population dynamics of wildlife, especially where census data do not exist for a species (Hargan et al. 2019). Similar to the migration of humans, the migration of sensitive species can be tracked through paleolimnological inferences of limnological conditions (Hobbs and Wolfe 2008). Six articles from our key word search discussed the application of paleolimnological methodologies in the realm of wildlife management. A reoccurring theme in these articles was reconstructing limnological conditions to assess and track how habitat conditions of endangered fish species have changed in freshwater lakes (Selbie et al. 2007; Ginn et al. 2008). As ecotones are expected to shift with an anthropogenic warming, employing paleolimnological techniques will be very valuable to understand wildlife population shifts and to better protect species against habitat threats. Ultimately, the history behind the evolution of natural systems is crucial for assessing conservation priorities (Zawiska et al. 2013).

While pollen analysis is commonly used in paleolimnological reconstructions, studies that specifically focus on changes in vegetation that may influence human society were less commonly found in the literature. Five of the 68 articles in our study focused on the application of paleolimnological methodologies for identifying the onset of new species (e.g., the introduction of invasive species), and (or) changes in climate and post-glacial hydrologic change with respect to vegetation cover. Paleolimnological methodologies are also useful to simply reconstruct changes in the dominant types of vegetation (Zhilich et al. 2017), which can ultimately provide reference conditions of a region for restoration projects to keep in mind.

The use of emerging techniques with an interdisciplinary focus, as well as transdisciplinary methods, have expanded our knowledge of human settlement. For example, the inclusion of zooarchaeological archives along with an analysis of lipid biomarkers and isotopic geochemistry of sediments allowed Connolly et al. (2019) to infer human settlement locations back to the Paleolithic (late Pliocene) era, providing evidence of some of the very first sites of human occupation. Indeed, as Smol (1990) noted, paleolimnology as a method in the realm of aquatic sciences has substantially advanced; we can still see that this holds as true in 2020 as it did in 1990. The number of publications on reconstructing subsistence cultures has increased dramatically in recent years (Fig. 1a). While our systematic mapping approach captured some new and novel approaches (such as Connolly et al. 2019), we undoubtedly missed studies that may have made inferences from lacustrine sediments using different methods deploying different terminology. For example, advances in fecal biomarkers (Guillemot et al. 2015; Zocatelli et al. 2017) and sedimentary DNA (Domaizon et al. 2017) have opened new and interesting opportunities for investigating long-term influences of humans on the environment. Yet, our systematic approach did not capture these studies, as they did not include key words associated with paleolimnology. Studies that are either primarily driven by an archaeological focus (e.g., Zocatelli et al. 2017), or based on former lacustrine sediment archives (Labarca et al. 2020) are particularly difficult to capture in a review of paleolimnological approaches; while they use lacustrine archives, they do so in a unique way for a completely different discipline. Indeed, our systematic map of literature notes that while paleolimnology can be used to infer the influence of climate on subsistence cultures, these inferences are often only made in a direct way when a combination of discipline-specific methods are deployed (e.g., archaeological evidence). The future of paleolimnological research may actually reside in the ability for researchers to have an interdisciplinary focus and combine innovative approaches to reconstruct past environments.