Surface water changes in the Norwegian Sea during last deglacial and Holocene times

Stable carbon and oxygen isotopes of the polar planktic foraminifera Neogloboquadrina pachyderma sinistral from sediment cores of the Norwegian Sea reveal several anomalous 13C and δ18O depletions in the surface water during the last glacial to interglacial transition and during the later Holocene. The depletions that are observed between the Last Glacial Maximum (LGM) and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs, which consequently resulted in a stratification of the uppermost surface water layer and a non-equilibrium between the water below and the atmosphere. At ~8.5 ka (14C BP) this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice-rafted detritus. After this time, the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers. However, this post-deglacial evolution towards a modern-type oceanographic environment was interupted by a hitherto undescribed isotopic event (~7–8 ka) which, on a regional scale, is only identified in eastern Norwegian Sea surface water. This event may be associated with the final pulse of glacier meltwater release from Fennoscandia, which affected the onset of intensified coastal surface water circulation off Norway during a time of regional sea-level rise. All these data indicate that surface water changes are an integral part of deglacial processes in general. Yet, the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later Holocene when from a climatic point of view relativelystable conditions prevailed

Late Neolithic and Chalcolithic maritime resilience? The 4.2 ka BP event and its implications for environments and societies in Northwest Europe

This paper deals with prehistoric communities at the end of the 3rd millennium BC in Northwest Europe in relation to the 4.2 ka BP climatic event. In particular, the question of the resilience of these communities to climatic change will be studied here by comparing various climatic records and analysing specific archaeological parameters for social and cultural change. These parameters include the duration and intensity of settlement occupation, the variability of subsistence activities (e.g. cereal cultivation, animal husbandry, hunting, fishing, and gathering) and the connectedness of communities within exchange networks. Rather than answering the often-asked yes/no question with regard to human–environment relations, our research asks what effect resulted from the 4.2 ka BP climatic event, and, from the perspective of resilience, how did communities adopt to these changes in their practices and cultural choices during the later 3rd millennium BC. In short, we maintain that climate change took place at the end of the 3rd millennium BC, but the changes in humidity and temperature with their effects on vegetation were probably regionally varied across Northwest Europe. We also observe that the studied communities developed differently during the second half of the 3rd millennium BC. On the one hand, we identify new food storage and house building techniques in the Low Countries and Schleswig-Holstein and, on the other hand, substantiate population decrease on the Orkney Islands around 2300 BC. Finally, we note a development of the Bell Beaker phenomenon into an Early Bronze Age maritory of connected communities across the North Sea, in which these communities expressed their resilience to climate change

Potential responses and resilience of Late Chalcolithic and Early Bronze Age societies to mid-to Late Holocene climate change on the southern Iberian Peninsula

In this investigation, we use a socio-environmental multi-proxy approach to empirically test hypotheses of recurrent resilience cycles and the role of climate forcing in shaping such cycles on the Iberian Peninsula during mid-Holocene times. Our approach combines time series reconstructions of societal and environmental variables from the southern Iberian Peninsula across a 3000 yr time interval (6000–3000 cal yr BP), covering major societal and climate reorganisation. Our approach is based on regional compilations of climate variables from diverse terrestrial archives and integrates new marine climate records from the Western Mediterranean. Archaeological variables include changes in material culture, settlement reconstructions and estimates of human activities. In particular, both detailed chronologies of human activities evolving from the Late Neolithic to the Bronze Age and mid- to Late Holocene climate change across the mid-Holocene are compared, aiming to assess potential human responses and coping processes associated with abrupt mid-Holocene climate changes

The Chalcolithic–Bronze Age transition in southern Iberia under the influence of the 4.2 kyr event? A correlation of climatological and demographic proxies

The end of the third millennium BCE represents (not only) on the Iberian Peninsula the time of transition to the Bronze Age. At the same time this is the time of a general climatic event, the so-called 4.2 ka BP event, which can be observed (in different manifestations) in different regions of the northern hemisphere. By synchronizing cultural and climatic developments and above all by assessing demographic developments and their spatial development, a much-discussed connection between the two phenomena can be made plausible and opens the perspective for further, more detailed research on the interdependence between cultural, demographic and climatological processes. For this purpose, the results of aoristics, 14C sum calibration and the evaluation of the concentration of long-chain n-alkane homologues of terrestrial origin as precipitation predictor are combined, their correlation is presented and possible responses are interpreted from the mapping of the settlement system development. This article provides an initial overview of the current results

Multi-decadal atmospheric and marine climate variability in southern Iberia during the mid- to late-Holocene

To assess the regional multi-decadal to multicentennial climate variability along the southern Iberian Peninsula during the mid- to late-Holocene record of paleoenvironmental indicators from marine sediments were established for two sites in the Alboran Sea (ODP-161-976A) and the Gulf of Cadiz (GeoB5901-2). High-resolution records of organic geochemical properties and planktic foraminiferal assemblages are used to decipher precipitation and vegetation changes as well as hydrological conditions with respect to sea surface temperature (SST) and marine primary productivity (MPP). As a proxy for precipitation change, records of plant-derived n-alkane composition suggest a series of five distinct dry episodes in southern Iberia at 5.4 +/- 0.3 ka cal BP, from 5.1 to 4.9 +/- 0.1 ka cal BP, from 4.8 to 4.7 +/- 0.1 ka cal BP, from 4.4 to 4.3 +/- 0.1 ka cal BP, and at 3.7 +/- 0.1 ka cal BP. During each dry episode the vegetation suffered from reduced water availability. Interestingly, the dry phase from 4.4 to 4.3 +/- 0.1 ka cal BP is followed by a rapid shift towards wetter conditions revealing a more complex pattern in terms of its timing and duration than was described for the 4.2 ka event in other regions. The series of dry episodes as well as closely connected hydrological variability in the Alboran Sea were probably driven by NAO-like (North Atlantic Oscillation) variability. In contrast, surface waters in the Gulf of Cadiz appear to have responded more directly to North Atlantic cooling associated with Bond events. In particular, during Bond events 3 and 4, a pronounced increase in seasonality with summer warming and winter cooling is found.DFG (German Research Foundation) CRC 1266 2901391021 Fundacao para a Ciencia e Tecnologia SFRH/BPD/111433/2015info:eu-repo/semantics/publishedVersio

Evidence for a steeper Eemian than Holocene sea surface temperature gradient between Arctic and sub-Arctic regions

Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs

Understanding climate resilience in Scandinavia during the Neolithic and Early Bronze Age

Mid and late-Holocene climate shifts are considered to have profoundly shaped demographic developments and adaptive responses of communities globally. Yet their onset, duration, and impact on Neolithic and Early Nordic Bronze Age communities in the high-latitude ranges of southern and north-western Scandinavia remain a major research gap. Here, we built on an emerging body of archaeological and paleoclimate data, encompassing 20,908 anthropogenic 14C dates and 49 climate records from the Holocene. Additionally, we gathered and correlated a new archaeological dataset of 3649 houses from southern Scandinavia and southern Norway. In this study, we utilised 6268 reliable 14C dates and 2519 dwellings to generate time series and socio-economic trends from ∼4100 to 1100 BCE. Our study revealed three key findings: (1) A distinct lateral zonation, with variations in the duration and timing of the Holocene Thermal Maximum (∼7050–2050 BCE). In Southern Scandinavia, a warmer climate may have facilitated the spread of crop cultivation (3820–3790 BCE), coinciding with significant population growth. Neolithic communities settled in permanent two-aisled houses 90–160 years later (3700–3660 BCE). (2) The 2250 BCE (4.2 ka BP) cooling trend marked the beginning of a climate regime shift with varying duration and timing (∼3450–1450 BCE). This period coincided with demographic growth, migration, crop cultivation diversity, and the development of houses with crop storage facilities (2290–2215 BCE). (3) Severe abrupt cooling periods (∼1850–1450 BCE) corresponded to short-term demographic decline including disruptions in trade networks with continental Europe. However, repopulation and redistribution of wealth (∼1450 BCE), along with the development of stable three-aisled houses (1475–1450 BCE), underscore the resilience of food-producing economies in mitigating environmental disturbances

Disentangling multiproxy temperature reconstructions from the subtropical North Atlantic

Reliable reconstruction of past sea surface temperature (SST) is of prime importance for understanding the Earth’s sensitivity to external forcing. Yet, it remains a major challenge in paleoceanography because comparison between SST estimates from different proxies reveals mismatches and raise the question as to what the contrasting proxies actually record. A better understanding of these mismatches in the light of seasonal occurrence of the proxy bearing organisms (archives) and water mass changes help to assess climate models. Here, we analyze data from the last deglaciation using a sediment core site situated at the northern boundary of the North Atlantic subtropical gyre influenced by fast latitudinal migrations of the subtropical Azores Front (AF) and resulting changes in water masses that may affect the SST records. Differences between the SST estimates from different deglacial SST reconstructions obtained from (1) Mg/Ca in planktic foraminifer tests, (2) alkenone UK′37, and (3) planktic foraminifer assemblages (SIMMAX), are assumed to result from the ecology of the proxy bearing organisms, and are assessed for the impact on different SST reconstructions from local seawater δ18O (δ18Ow) reconstructions. The general trends of SSTs from all four proxies confirm the well-known deglacial succession of warm and cold events. Mismatches between amplitudes of temperature changes are explained by differences in the phenology of the proxy-bearing organisms and local changes in hydrography. The combination of δ18O SST from the three different archives of δ18Ow reconstructions may cause offsets that exceed the climate driven signals