The influence of Holocene sea-ice variability on Arctic biota: using the past to predict the future

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Sea ice provides an important seasonal or perennial habitat and dispersal corridor for many Arctic species and acts as a major geographic barrier for others; it therefore influences the distributions, gene flow, and species interactions of marine and terrestrial biota. The Arctic Ocean is predicted to become seasonally ice-free this century as a result of climate change. The ecological and evolutionary consequences of this change remain poorly understood, although species with a high reliance on sea ice to complete their life histories are likely to be particularly vulnerable. Our ability to quantify the impacts of sea ice loss is hampered by our limited understanding of how species respond to long-term spatial and temporal variation in sea ice. This is due to a shortage of historic and modern observational data for many species, as well as sparse data on the natural variability of sea ice since the Last Glacial Maximum, although high-resolution sea ice reconstructions are emerging. Another challenge is to improve attribution of sea ice as the primary driver of species dynamics, as many associations remain speculative due to lack of appropriate sea ice and/or biotic data, in many cases not even using sea ice data at all.This project aims to advance predictions of impacts of current sea ice loss by improving our understanding of the long-term interactions between sea ice and Arctic species, specifically: how sea ice variability influenced Arctic biota during the Holocene (11,700 years - present). The three main areas of study are:i. What is the spatiotemporal history of selected ice-associated species during the Holocene?ii. What is the relationship between sea ice and Arctic species dynamics in the Holocene?iii. How does sea ice continue to influence plant dispersal in the Arctic, and how do modern plant dispersal pathways compare with reconstructed dispersal pathways?A pre-analysis systematic review of which species are most dependent on sea ice, and which are therefore most likely to be at risk from sea ice loss, will help inform selection of focal species and help generate hypotheses. The project will use emerging high-resolution driftwood-based reconstructions of Holocene Arctic sea ice (Hole & Macias-Fauria, 2017) which will give detailed information on the natural variability of sea ice dynamics. For question (i), ancient DNA from fossils and modern molecular data will be compiled to reconstruct and model species dynamics using: population genetic analysis (demographic change, population connectivity, and genetic diversity) and species distribution modelling (range shifts and dispersal events). For (iii) the project will combine reconstructions of sea ice and species dynamics to assess causality from the spatiotemporal patterns of covariability. The analysis will also account for other possible sources of variation in species dynamics, for example: other aspects of climate, geography, and biotic interactions. In addition, species dynamics may also be impacted by increasing human-driven pressures in the Arctic, as a result of its increasing accessibility. Question (iv) will entail fieldwork analysing plant material that is deposited by coastal sea ice on Svalbard beaches. This will involve collection, identification, and viability-testing of propagules, identification of possible source regions, and an analysis of whether modern dispersal pathways agree with the spatiotemporal histories of the study plants. There is potential to develop a citizen-science project in collaboration with the Environment Department of the Svalbard Governor.The results from this project will reveal the extent to which sea-ice has historically influenced Arctic biota, and give insights into potential ecological and evolutionary responses to current sea ice loss; thereby enabling more accurate predictions of the impacts of climate change in the Arctic.