A transforming Arctic - Unraveling Climate Change Impacts on Sea-Ice Evolution and Oceanic pCO2
Fig 1.2. Bathymetric map of the Arctic with an overview of the different Arctic regions used in this study.Abstract
The Arctic undergoes profound transformations due to global warming, with climate change impacts varying at regional levels. While many changes, such as declining sea ice and alterations in ocean biochemistry, are often discussed based on the pan-Arctic average, their local implications and intensity variations across regions have been largely overlooked, despite their importance for stakeholders. This thesis aims to help shift the perspective towards understanding regional changes in the Arctic by investigating two crucial indicators affected by a warming climate: Arctic sea-ice coverage and surface ocean partial pressure of carbon dioxide (pCO2 ). The first is of interest to a variety of stakeholders, particularly to those interested in changes along the coast–ice transition zone, such as the shipping industry and indigenous people. The latter is a key factor in the exchange of CO2 between ocean and atmosphere and is, therefore, decisive for the acidification of the oceans. The sensitivity of sea-ice area to near-surface air temperature changes, i. e. how strongly sea-ice area diminishes for a given rise in temperature, exhibits a high seasonal dependence, characterized by significant variability in summer and low variability in winter. This study reveals that the transition between summer and winter, along with the observed low variability in winter, can be attributed to the geographic blocking of the sea-ice edge by surrounding land masses. By quantifying the timing of the blocking, the analysis links the timing changes to rising global temperatures. The findings indicate that as the timing shifts and the season during which the ice edge is blocked shortens (by around 7 days per tenth degree of global warming on average), adjacent seasons will experience heightened sensitivity in sea-ice area. Particularly, sensitivities in areas along the coasts of the high Arctic Ocean will undergo a sudden change in the future. Expanding the sensitivity analysis to a regional scale, the study provides new perspectives on how the sea ice in individual Arctic regions responds to global warming, anticipating future changes. The East Siberian Sea, the Chukchi Sea, and the Laptev Sea are identified as regions likely to lose their summer sea ice first. The Barents Sea is projected to become the first region to lose its remaining winter sea ice, ultimately becoming ice-free year-round. Shifting focus to surface ocean pCO2, two data products estimating surface ocean pCO2 to fill the sparse observations in the Arctic are used to investigate the evolution of surface ocean pCO2 in the Arctic domain. Both products reveal consistent increases in most regions over the last two decades. However, substantial differences in the magnitudes of inter- and intra-annual changes are observed between the two datasets. Separating the spatial and temporal variability in the pCO2 via EOF analysis reveals the dominant drivers of changes in the pCO2 in different domains of the Arctic. The study identifies sub-Arctic domain changes primarily related to the seasonal solar irradiance cycle, while high Arctic pCO2 changes are dominated by changes in sea-ice cover. Examining seasonality, shifts and changes in intra-annual amplitude are noted already in the historical record, particularly north of Canada, indicating potential impact on ecosystems. This thesis underscores the necessity of taking a regional perspective on Arctic climate change. By systematically analyzing and quantifying the blocking effect for the first time, it provides a foundation for understanding sea-ice area changes in the high Arctic, benefiting stakeholders interested in Arctic Ocean transformations, particularly in coastal regions. Additionally, the pCO2 analysis offers insights into the drivers of pCO2 in the Arctic Ocean, serving as a benchmark to enhance future data products, crucial for investigating regional changes in the Arctic surface ocean carbon cycle. These findings contribute to the groundwork for future research in the Arctic.
