The North Atlantic Oscillation forcing through the last 2000 years: Spatial variability as revealed by high-resolution marine diatom records from N and SW Europe (original) (raw)
Related papers
Boreas, 2011
Stable isotopes from benthic foraminifera, combined with diatom assemblage analysis and diatom-based sea-surface salinity reconstructions, are used for the interpretation of changes in bottom-and surface-water conditions through the early Eemian at Ristinge Klint in the western Baltic Sea. Correlation of the sediments with the Eemian Stage is based on a previously published pollen analysis that indicates that they represent pollen zones E2-E5 and span $3400 years. An initial brackish-water phase, initiated c. 300 years after the beginning of the interglacial, is characterized by a rapid increase in sea-surface and sea-bottom salinity, followed by a major increase at c. 650 years, which is related to the opening of the Danish Straits to the western Baltic. The diatoms allow estimation of the maximum sea-surface salinity in the time interval of c. 650-1250 years. After that, slightly reduced salinity is estimated for the interval of c. 1250-2600 years (with minimum values at c. 1600-2200 years). This may be related to a period of high precipitation/humidity and thus increased freshwater runoff from land. Together with a continuous increase in the water depth, this may have contributed to the gradual development of a stratified water column after c. 1600 years. The stratification was, however, particularly pronounced between c. 2600 and 3400 years, a period with particularly high sea-surface temperature, as well as bottom-water salinity, and thus a maximum influence of Atlantic water masses. The freshwater runoff from land may have been reduced as a result of particularly high summer temperatures during the climatic optimum.
Eemian Climatic and Hydrographical Instability on a Marine Shelf in Northern Denmark
Quaternary Research, 1997
tion of the foraminifera, show the stable isotope data for the Benthic foraminifera and stable isotope data from the last interfirst time, and discuss substage 5e in relation to the Holocene glaciation (Eemian, substage 5e) from a borehole at Skagen, Denin the same area. mark, provide evidence for major environmental and hydrographic changes during this period. During the first millennium SETTING of the Eemian, water masses covering northern Denmark became gradually warmer. Temperate conditions prevailed during most of the interglaciation, but these were interrupted by two periods Skagen is the site of a late Quaternary marine embayment with decreased water temperatures. The first cooling (Event S-1) up to 300 m deep, the Kattegat Depression, which stretched was not very distinct at Skagen, but the second (Event S-2), seen as a southern extension of the deep Norwegian Trench across in both the foraminiferal and oxygen isotope record, represents a northern Denmark and into the Kattegat during the last interlarge shift to subarctic conditions. Carbon isotopes indicate a glaciation . This basin was change in ocean circulation during both events. No comparable gradually filled with sediments from the late Saalian through climate variations are seen within the Holocene record at the site. to the Holocene. Combined with isostatic uplift of Denmark The final cooling of the water masses associated with the substage this resulted in a significant shallowing of the Kattegat and 5e/5d boundary occurred within a few hundred years. These last raising of northern Denmark above sea level. interglacial climatic changes were probably caused by variations Skagen Spit, the northernmost part of Denmark, divides in strength and/or position of the North Atlantic Drift, possibly the Kattegat and Skagerrak Seas (Figs. 1, 2). The spit formed as a result of varying vigor of the Atlantic conveyor. In addition, minor variations in the fossil assemblages also indicate fluctuations gradually since the beginning of the Holocene (Hauerbach, in the inflow of Atlantic water to the Skagerrak-Kattegat area 1992), and though the site of the Skagen 3 boring during the warm intervals of substage 5e. ᭧ 1997 University of Washington. at present is above sea level, it was covered by the sea during substage 5e and during most of the late Weichselian (late stage 2) and the Holocene (Conradsen and Heier-Nielsen, 218
Late Holocene coastal hydrographic and climate changes in the eastern North Sea
Holocene, 2006
We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.
Baltica, 2012
Baltic Sea water exchange is primarily governed by atmospheric forcing of the inflow of saline waters by strong westerly winds prevailing over the central North Atlantic and northwestern Europe. Our sediment core study uses geochemical element records indicative of phytoplankton and cyanobacterial blooming as well as continent-derived mineral input for reconstructing hydrographic changes in the deeper Baltic Sea basins around AD 1200. An alkenone-based Sea Surface Temperature (SST) reconstruction for the relevant time span, AD 500-1500, is presented for another sediment core obtained from the shallow Isefjord located at the southern coast of the Kattegat at the entrance of the Baltic. At the termination of the Medieval Climate Anomaly at approximately AD 1200, the basin sediment facies and the geochemical records reveal an environmental change indicative of a marked decrease of inflow activity and marine productivity. This change coincides with a SST decrease and recently reported general fall in Kattegat sea level. A comparison with palaeo-climate data from the wider North Atlantic region demonstrates that this regime shift in Baltic Sea water exchange is linked to a large-scale change in ocean and atmosphere circulation from a dominating, positive North Atlantic Oscillation (NAO+) mode to more negative NAO conditions.
Holocene Hydrographic Variations From the Baltic‐North Sea Transitional Area (IODP Site M0059)
Paleoceanography and Paleoclimatology, 2020
Deoxygenation affects many continental shelf seas across the world today and results in increasing areas of hypoxia (dissolved oxygen concentration ([O 2 ]) <1.4 ml/L). The Baltic Sea is increasingly affected by deoxygenation. Deoxygenation correlates with other environmental variables such as changing water temperature and salinity and is directly linked to ongoing global climate change. To place the ongoing environmental changes into a larger context and to further understand the complex Baltic Sea history and its impact on North Atlantic climate, we investigated a high accumulation-rate brackish-marine sediment core from the Little Belt (Site M0059), Danish Straits, NW Europe, retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347. We combined benthic foraminiferal geochemistry, faunal assemblages, and pore water stable isotopes to reconstruct seawater conditions (e.g., oxygenation, temperature, and salinity) over the past 7.7 thousand years (ka). Bottom water salinity in the Little Belt reconstructed from modeled pore water oxygen isotope data increased between 7.7 and 7.5 ka BP as a consequence of the transition from freshwater to brackish-marine conditions. Salinity decreased gradually (from 30 to 24) from 4.1 to~2.5 ka BP. By using the trace elemental composition (Mg/Ca, Mn/Ca, and Ba/Ca) and stable carbon and oxygen isotopes of foraminiferal species Elphidium selseyensis and E. clavatum, we identified that generally warming and hypoxia occurred between about 7.5 and 3.3 ka BP, approximately coinciding in time with the Holocene Thermal Maximum (HTM). These changes of bottom water conditions were coupled to the North Atlantic Oscillation (NAO) and relative sea level change. Plain Language Summary The Baltic Sea is an intracontinental sea connected to the North Atlantic Ocean with large economic and societal values. It is sensitive to salinity and temperature changes and low oxygen conditions in the bottom water. The Little Belt is a transitional area between the central Baltic Sea and the North Sea. It is an ideal area to study the changes of freshwater outflow and saline water inflow and how the dynamics vary in relation to larger-scale climate changes. We have reconstructed past seawater conditions (e.g., temperature, salinity and oxygenation) in the Baltic by geochemically analyzing microfossil (foraminifera) shells. We analyzed the trace elemental concentration and stable oxygen and carbon isotopes in calcite shells of low-oxygen tolerant foraminiferal species as well as the benthic foraminiferal assemblages from a sediment core originating from the Little Belt covering the past 7,700 years. The salinity increased dramatically~7,700-7,500 years ago and decreased~4,100-2,500 years ago. Variation in bottom water oxygen content and bottom water temperature coincide. Our study highlights the benefit of using modern marine monitoring data together with a multiproxy approach to establish the link between local hydrographic conditions and regional climate changes and to explain how the environment has developed over time.
With 5 fi gures in the text HASS, H. C. & KAMINSK I, M. A. (1995): Change in atmospheric and oceanic circulation reflected in North Sea sediments du ring the late Ho-locene.-Zbl. Geo!. Paiaont. Teil I, 1994 (1/2): 51-65; Stuttgart. Abstract: The results from twO of a total of four long sediment cores fr om high accumulation areas of the southern flank of the Skagerrak (NE North Sea) are given to further elucidate the interplay of atmospheric and ocean current circulation during the past ca. 1300 years. Strong westerlies, emerging from the Northern Hemisphere main westerly wind stream (MWWS), are likely t o amplify current intensities, while easterly wind directions can hamper the water mass circulation in the Skagerrak. Changes in c urrent energies can be traced by the granulo-metric composition of the sediments. Earlier invest igat ions regarding the movement of the cyclone tracks (northwards during wa rm and southwards during cold per iods; see e. g. LAMB 1969) can be confirm ed: the Medieval War m Period (ca. 800/1000-1350 AD) is characterized by gene rally finer sediments indicating lower bottom cu rrent energies. Thus, minor wind-forcing and a no rthern position of the MWWS can be inferred. During the Little Ice Age (ca. 1350-1900 AD) a southwa rd movement of the MWWS as fa r south as the Skagerrak system and probably further south can be traced. Zusammenfassung: Am Beispiel zweier von vier langen Sedimentkernen aus Hochakkumula tionsgebieten der Sudflanke des Skagerraks (NE-Nordsee) wird das Zusammenspiel von atmospharischen und Wassermassenzirkula-tionsmustern wahrend der letzten ca. 1300 Jahre da rgest e llt. Starke Winde der nordhemispharischen Westwinddrift (MWWS) sind in der Lage, die Wassermassenzirkulation im Skage rrak zu verstarken, wahrend Winde aus astlichen Richtungen die Zirkulation behindern konnen. Ver-iinderungen in der ' Stromungsenergie dokumentieren sich dUTch Veriinde-rungen in der granulometrischen Zusammensetzung der Sedimente. F riihere Untersuchungen der N-S-Bewegungen de r Zyklonenzugbahnen (nordwiirts wiihrend warmer und sudwarts wahrend kalter Klimaperioden;
A mid-Holocene geochemical record of salt water inflow to the Baltic Sea.
The formation of Mn-enrichments in Gotland Deep sediments has been linked to the occurrence of periodic inflows of saline water from the North Sea. In turn these saline inflow events are very strongly linked to variation in North Atlantic atmospheric conditions. Here we measure sedimentary Mn-concentrations in mid Holocene sediments with a 0.5mm sampling resolution using scanning electron microscope techniques. As the sedimentation rate in core 20001-5 was estimated to be approximately 0.5-1mm per year, examining the variation in Mn-enrichments may potentially provide an annual record of variation in saline inflow, and by extension, North Atlantic climate on interannual timescales. Processes that can affect Mn-cycling in the Gotland Deep were considered together producing a complex web of factors. These could potentially act to remove or significantly weaken the transmission of the primary saline inflow signal to the measured geochemical record, producing an effectively random Mn-record. Analysing the Mn-record as a time series of discrete events revealed that the Mn-record was not consistent with a random distribution of events, and contains some long term order. Spectral analysis of the Mn-record then indicates a significant periodicity in the Mn-record between 33-35.5mm. This represents a discrete decadal periodicity in Mn-enrichment at between 25-55 years that is consistent with the timing of previously reported Mn-enrichments in Gotland Deep sediments.