Eystein Jansen’s research while affiliated with University of Bergen and other places

To better understand the processes in the Nordic Seas and their connection to large-scale climate changes during Dansgaard-Oeschger (D-O) events, we reconstruct sea ice extent (SIE) and subsurface temperatures (SubSTs) in the eastern Fram Strait between 40 and 33.5 ka b2k. Our new proxy data from MD99-2304 reveal pronounced fluctuations in SIE and SubSTs both between and within each investigated Greenland Stadial (GS) and Greenland Interstadials (GIs). Consequently, 15 variations in SIE and SubSTs in the eastern Fram Strait show a weaker connection to climate oscillations in Greenland ice cores, in comparison to changes observed in the southeastern Nordic Seas and the North Atlantic. Integrating our results with AMOC strength reconstructions and sea ice records from the southeastern Nordic Seas, we identify different sea ice regimes between the eastern Fram Strait and the southeastern Nordic Seas. These findings suggest that fluctuations in the eastern Fram Strait were primarily driven by shifts in northward oceanic heat transport, which were 20 regulated by changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC).

The South African coastline hosts archaeological sites related to the hominid evolution and the first modern humans. This region has been strongly shaped by a series of sea level fluctuations resulting in multiple exposures of South Africa’s continental shelf. However, there is limited knowledge regarding the main paleoclimatic drivers behind sea level variability and the presence and distribution of Early to Late Stone Age open-air sites in the continental interior. Our research aims to uncover the trigger mechanism linked to sea transgressive and regressive phases during the Middle Stone Age period (120-50 ka) and its impact on the coastal landscape. Moreover, our research aims to study the distribution and evolution of paleowetlands systems and their possible implications with the dynamics of the Early to Late Stone Age hunter-gatherers groups in the continental interior.

Sea ice conditions in the eastern Fram Strait between 40 and 36.5 ka b2k (thousand years before the year 2000) are reconstructed in detail, based on biomarker analyses. Following extensive sea ice conditions around the Greenland Interstadial 9/Greenland Stadial 9 transition at 39.9 ka b2k, repeated polynya activity marked Greenland Stadial 9 in the eastern Fram Strait. Nearly perennial sea ice was observed around the Greenland Stadial 9/Greenland Interstadial 8 transition at 38.22 ka b2k, followed by a gradual establishment of seasonal sea ice cover over the research area during Greenland Interstadial 8. Previous studies highlighted sea ice retreat in the southeastern Nordic Seas as a driver of abrupt Greenland Stadial to Interstadial climate change. We document intervals with less sea ice in the eastern Fram Strait during Greenland Stadial 9 and Interstadial 8 than previously suggested. By mapping the variable sea ice extent during Greenland Stadial 9 and Interstadial 8, further constraints are detected that may help define the role of the Nordic Seas sea ice cover in driving abrupt climate change during glacial times.

During the late Quaternary the past climatic conditions of southern South Africa underwent fluctuations, influenced by various climatic factors, such as the impacts of both the Indian and Atlantic Oceans, as well as the effects of the southeasterly trade winds and Southern Hemisphere Westerlies (SHW), influenced by changes in orbital parameters. At the same time, this region exhibits some of the most abundant Middle Stone Age (MSA) archaeological sites containing records of Homo sapiens behavioural and technological evolution. Consequently, there is a pressing need for precise climatic reconstructions that can provide climate constraints during the MSA in this area. However, there is a lack of continuous high-resolution climate records covering the majority of the MSA, which spans from ~300 to ~60 ka. In this study, we present data obtained from a marine sediment core (MD20-3592) that spans approximately the last 260,000 (from m8 to 1) aiming to expand the spatial and temporal coverage of available climate archives. This marine sediment core documents both terrestrial and ocean hydroclimate variability because it is strategically positioned close to the South African coastline receiving terrestrial sediments via riverine input as well as being located under the marine influence of the Agulhas Current at the same time. X-ray fluorescence (XRF) core scanning, calibrated with discrete samples analyzed by XRF spectroscopy, was used to determine the variability of the bulk elemental composition of the core over time. Principal component analysis was performed to facilitate the interpretation of the data. Statistical analyses including frequency analysis, gaussian filtering, and wavelet analysis reveal that the regional hydroclimate was affected mostly by local insolation changes caused by orbital precession, and high latitude forcing that varies on timescales associated with orbital obliquity and eccentricity. Increased fluvial input was associated with a high precession index, during times of high local insolation, due to the effects of precession on local convergence and seasonal rainfall. Comparison with regional climate archives confirmed the dominant influence of precession on precipitation in southern South Africa. On glacial-interglacial timescales, lower precipitation observed during glacial intervals could be explained by a northward shift of the Southern Hemisphere Westerlies (SHW) and South Indian Ocean convergence zone (SIOCZ). Finally, the data from core MD20-3592 can provide a climatic context for the appearance of behavioral complexity in South Africa between ~ 120 ka and ~ 50 ka. Humid conditions in the river catchments going through the south coast and south-east coast of South Africa were present at approximately 117 ka, 93 ka, and 72 ka, alternating with dry conditions at approximately 105 ka, 83 ka, and 60–50 ka.

In southern Africa, past landscape conditions could play a relevant role in the evolution of anatomically modern humans and their dispersal through the continental interior. The southern African landscape comprises coastal areas, fluvial floodplains, pan systems, and caves. Therefore, every landscape could offer an opportunity or challenge to modern humans during their dispersal. This research intends to shed light on one central question: How was the paleo-landscape that our ancestors inhabited? To reach this aim, diverse landscapes will be studied. Coastal landscape and Agulhas Bank Our research aims to investigate the factors that led to transgressive and regressive sea phases during the Middle Stone Age period (120-50 ka). We will examine how these phases impacted the continental landscape features of the Agulhas Bank and explore the potential connection between these events and the human presence in the Blombos Cave. Continental interior We will study the landscape evolution of the western Little Karoo, potentially employed as an inland dispersal corridor by hunter-gatherer groups. This region includes diverse pan systems, fluvial floodplains, dune systems and caves.

Linking human technological and behavioural advances to environmental changes is challenging, as it requires a robust understanding of past climate at local scales. Here, we present results from regional high-resolution numerical simulations along with climate data directly from the archaeological sequence of Blombos Cave (BBC), a well-studied site in coastal southern Africa. The model simulations cover two distinct periods centred at 82 and 70 thousand years (ka) ago (Marine Isotope Stage [MIS] 5 and the onset of MIS 4, respectively), when orbital parameters and global sea level were markedly different from one another. Climatic changes from 82 to 70 ka are determined through four simulations that use past and present-day coastline configurations. The hydrogen isotopic composition of leaf waxes (δ²Hwax) and n-alkane distributions and abundances are used to reconstruct hydroclimate around BBC. The leaf wax n-alkane record, one of the first produced in an archaeological setting in this region to date, can be interpreted as a drying signal from MIS 5c to 4. This agrees with our modelling results, which indicate a drier and more continental climate over coastal southern Africa at 70 ka, compared to 82 ka. The simulated aridification is most evident from the reduced precipitation amounts in both summer (∼20%) and winter (∼30%). The annual number of summer days (Tmax ≥ 25 °C) and cold nights (Tmin < 5 °C) in the vicinity of BBC increases more than 5 and 3-fold, respectively, under the more continental climate at 70 ka. Weaker westerly winds in winter, a cooler Agulhas Current, and a land surface expansion associated with the coastline shift due to lower sea levels at 70 ka all contribute to the simulated climate shift. Our approach highlights the importance of multiple lines of evidence for achieving robust results, while demonstrating how both large-scale forcing and local influences worked together in shaping the local climate that early humans lived in. Adaptation to a drier climate and increased continentality around BBC might have induced greater mobility, which led to increased population interactions, cultural transmission rates, skill exchange, and material complexity during the so-called Still Bay period.

We combine consistently dated benthic carbon isotopic records distributed over the entire Atlantic Ocean with numerical simulations performed by a glacial configuration of the Norwegian Earth System Model with active ocean biogeochemistry in order to interpret the observed Cibicidesδ13C changes at the stadial–interstadial transition corresponding to the end of Heinrich Stadial 4 (HS4) in terms of ocean circulation and remineralization changes. We show that the marked increase in Cibicidesδ13C observed at the end of HS4 between ∼2000 and 4200 m in the Atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high-latitude glacial North Atlantic. Our model results show that this Cibicidesδ13C signal is associated with changes in the ratio of southern-sourced (SSW) versus northern-sourced (NSW) water masses at the core sites, whereby SSW is replaced by NSW as a consequence of the resumption of deep-water formation in the northern North Atlantic and Nordic Seas after the freshwater input is halted. Our results further suggest that the contribution of ocean circulation changes to this signal increases from ∼40 % at 2000 m to ∼80 % at 4000 m. Below ∼4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of HS4. The simulated lower remineralization during stadials compared to during interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep Southern Ocean during stadials found in previous studies.

Over recent decades, the rate of global mean sea-level rise has increased, although the magnitude—tens of centimetres—remains small from a geological perspective. Such a modest rise in sea level presents a challenge when attempting to assess its global climate impacts, as the signal is weak. However, in previous warmer geological periods, sea levels reached up to tens of metres higher than the present levels. These palaeoclimate periods offer a unique opportunity to investigate the climate effects of higher sea levels. Here, using climate simulations of the Last Interglacial period and a set of present-day sea-level sensitivity experiments, we highlight the importance of global mean sea-level rise in modulating global climate. The lowering of terrestrial elevation and deepening of oceanic bathymetry due to a spatially uniform rise in sea level reorganizes atmospheric and oceanic circulations. Our simulations of the Last Interglacial show that considering this aspect of global mean sea-level rise in isolation from changes associated with land–sea masks or freshwater input reduces the long-lasting model–data mismatch in the Southern Hemisphere. Furthermore, the present-day sensitivity experiments demonstrate that a slight increase in global mean sea level causes substantial adjustments in the global climate, particularly at mid–high latitudes.

Paleoclimatic changes in South Africa, especially around the southern Cape region, are of intense interdisciplinary interest; as this is an important area in the context of human evolution, hosting several prominent archaeological sites such as Blombos Cave (located near today's shoreline). In this study, we investigate the sensitivity of climate of coastal southern Africa to changes in glacial variations in sea level and associated land extent, by performing a model sensitivity experiment. Employing a high-resolution (12 km grid spacing) regional climate model (WRF), output from a global model simulation at 70 thousand years ago (ka) is downscaled twice: First using the present-day coastline, then with an estimated coastline position at 70 ka; keeping all other forcing factors identical. Thus we focus on the response of the local climate to an expanded land surface area equivalent to a glacial sea level low stand scenario. Our results reveal that the climate of previously coastal localities shows strong continental characteristics when sea level drops, as the coastline moves away, and a coastal plain is exposed. This is most evident from the year-round warmer days and cooler nights, with up to 6 °C increases (decreases) in daily maximum (minimum) temperatures. This result also extends to extremes. For instance, at the archaeological site of Blombos Cave, temperature extremes (1st and 99th percentiles) of the modelled marine climate become 25- to 75-fold more probable as the coastline shifts. We also find year-round reductions (5–40%) in the amount of precipitation within the region, owing to local modifications in near-surface atmospheric circulation caused by the exposed land. The reductions in precipitation are accompanied by a significant drop in the annual number of rainy days (31 days locally at Blombos Cave). Simulated changes also vary seasonally, with more pronounced and widespread changes in temperature and precipitation occurring during summer. Through isolating and quantifying the effects of land extent variation, our approach demonstrates, for the first time, the role of coastline position in shaping local climate around near-coastal environs. Our results have significant implications for future studies exploring the influence of local coastline changes on early human settlement and mobility patterns.

We combine consistently dated benthic carbon isotopic records distributed over the entire Atlantic Ocean with numerical simulations performed by a glacial configuration of the Norwegian Earth System Model with active ocean biogeochemistry, in order to interpret the observed Cibicides δ13C changes at the stadial-interstadial transition corresponding to the end of Heinrich Stadial 4 (HS4) in terms of ocean circulation and remineralization changes. We show that the marked increase in Cibicides δ13C observed at the end of HS4 between ~2000 and 4200 m in the Atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high latitude glacial North Atlantic. Our model results show that this Cibicides δ13C signal is associated with changes in the ratio of southern-sourced (SSW) versus northern-sourced (NSW) water masses at the core sites, whereby SSW is replaced by NSW as a consequence of the resumption of deep water formation in the northern North Atlantic and Nordic Seas after the freshwater input is halted. Our results further suggest that the contribution of ocean circulation changes to this signal increases from ~40 % at 2000 m to ~80 % at 4000 m. Below ~4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of HS4. The simulated lower remineralization during stadials than interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep Southern Ocean during stadials found in previous studies.