NEW HIGH-RESOLUTION ALKENONE RECORD OF LAST GLACIAL TO HOLOCENE SEA-SURFACE TEMPERATURE CHANGE IN THE EAST-EQUATORIAL SOUTH ATLANTIC OCEAN

ABSTRACT. A new high-resolution, alkenone-de-rived record of sea-surface temperature (SST) change covering the last 26000 years was obtained from the east-equatorial Atlantic off the Congo River. Temperature fluctuations correspond to climate change recorded in other marine and terrestrial archives of the region. The maximum temperature difference between 26000 years BP ago and the Holocene climate optimum around 6000 years BP was 4.3°C, corroborating other SST estimates from the same area. The coldest conditions were followed by a warming that began at 24000 calendar years BP, a time when Northern Hemisphere ice sheets were still at their maximal position. This comparatively early warming is in agreement with previous findings from the east-equatorial South Atlantic. After a relatively stable period between 21500 and 14500 calendar years BP, a second warming began at 14500 calendar years BP which coincides with the onset of the African Humid Period. A cool period at 11500 calendar years BP halted this warming but the trend of increasing temperatures began again at 10000 calendar years BP, this time through large-scale oscillations. The warmest time, around 6000 calendar years BP, was followed by a modest cooling that coincides with the end of the African Humid Period and the onset of Neoglaciation on the African continent. Following this the record shows two distinct warming-cooling cycles during the late Holocene.     

Process length variation in cysts of the dinoflagellate Protoceratium reticulatum,from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy

Mertens, K. N., Dale, B., Ellegaard, M., Jansson, I.‐M., Godhe, A., Kremp, A. & Louwye, S. 2010: Process length variation in cysts of the dinoflagellate Protoceratium reticulatum, from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy. Boreas, 10.1111/j.1502‐3885.2010.00193.x. ISSN 0300‐9483. Results are presented from a regional comparison of average process length variation in cysts of Protoceratium reticulatum and Lingulodinium polyedrum, extracted from surface sediments in the Skagerrak–Kattegat–Baltic estuarine system, with the environmental variables of seawater temperature and salinity. Although too few cysts of Lingulodinium polyedrum were recovered from the sediments to make reliable correlations, cysts of Protoceratium reticulatum were well represented, and average process length was correlated significantly with both salinity and temperature. Owing to dominant summer surface production, and regional covariation between salinity and density, we propose the use of the significant correlation with summer sea surface salinity (SSS_summer) by the equation SSS_summer=3.16 × average process length ?0.84 (R²=0.8). Application of this equation down‐core in Limfjord (northern Denmark) shows its usefulness as a regional palaeosalinity proxy.     

POTENTIAL EFFECTS OF CLIMATE CHANGE ON FRESHWATER ECOSYSTEMS OF THE NEW ENGLAND/MID-ATLANTIC REGION

Numerous freshwater ecosystems, dense concentrations of humans along the eastern seaboard, extensive forests and a history of intensive land use distinguish the New England/Mid-Atlantic Region. Human population densities are forecast to increase in portions of the region at the same time that climate is expected to be changing. Consequently, the effects of humans and climatic change are likely to affect freshwater ecosystems within the region interactively. The general climate, at present, is humid continental, and the region receives abundant precipitation. Climatic projections for a 2 × CO₂ atmosphere, however, suggest warmer and drier conditions for much of this region. Annual temperature increases ranging from 3–5°C are projected, with the greatest increases occurring in autumn or winter. According to a water balance model, the projected increase in temperature will result in greater rates of evaporation and evapotranspiration. This could cause a 21 and 31% reduction in annual stream flow in the southern and northern sections of the region, respectively, with greatest reductions occurring in autumn and winter. The amount and duration of snow cover is also projected to decrease across the region, and summer convective thunderstorms are likely to decrease in frequency but increase in intensity. The dual effects of climate change and direct anthropogenic stress will most likely alter hydrological and biogeochemical processes, and, hence, the floral and faunal communities of the region's freshwater ecosystems. For example, the projected increase in evapotranspiration and evaporation could eliminate most bog ecosystems, and increases in water temperature may increase bioaccumulation, and possibly biomagnification, of organic and inorganic contaminants. Not all change may be adverse. For example, a decrease in runoff may reduce the intensity of ongoing estuarine eutrophication, and acidification of aquatic habitats during the spring snowmelt period may be ameliorated. Recommendations for future monitoring efforts include: (1) extending and improving data on the distribution, abundance and effect of anthropogenic stressors (non-point pollution) within the region; and (2) improving scientific knowledge regarding the contemporary distribution and abundance of aquatic species. Research recommendations include: (1) establishing a research centre(s) where field studies designed to understand interactions between freshwater ecosystems and climate change can be conducted; (2) projecting the future distribution, activities and direct effects of humans within the region; (3) developing mathematical analyses, experimental designs and aquatic indicators that distinguish between climatic and anthropogenic effects on aquatic systems; (4) developing and refining projections of climate variability such that the magnitude, frequency and seasonal timing of extreme events can be forecast; and (5) describing quantitatively the flux of materials (sediments, nutrients, metals) from watersheds characterized by a mosaic of land uses. © 1997 John Wiley & Sons, Ltd.     

EFFECTS OF CLIMATE CHANGE ON THE FRESHWATERS OF ARCTIC AND SUBARCTIC NORTH AMERICA

Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO₂ scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect of the environment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water supply of lakes in delta regions and which determines the availability of habitat for aquatic organisms. Climate warming or river damming and diversion would probably lead to the complete drying of many delta lakes. Climate warming would also change the characteristics of ponds that presently freeze to the bottom and result in fundamental changes in their limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the chemical, mineral and nutrient status of lakes and most likely have deleterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive. Extensive wetlands and peatlands are an important component of the global carbon budget, and warmer and drier conditions would most likely change them from a sink to a source for atmospheric carbon. There is some evidence that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation patterns; to model the thermal behaviour of wetlands, lakes and rivers; to understand better the interrelationships of cold region rivers with their basins; to begin studies on the very large lakes in the region; to obtain a firm grasp of the role of northern peatlands in the global carbon cycle; and to link the terrestrial water balance to the thermal and hydrological regime of the polar sea. Overall, there is a strong need for basic research and long-term monitoring. © 1997 John Wiley & Sons, Ltd.     

Storegga tsunami deposits in a coastal lake on Suouroy, the Faroe Islands

Presumed deposits of the Storegga tsunami have been recognized in a coastal lake situated 4 m a.s.l. on the island of Suðuroy, the Faroe Islands. The stratigraphy in the lake reveals a major erosion and redepositional event. The deposited material ranges from sand and sandy gyttja, with marine shell fragments and foraminifera, to gyttja with rip-up clasts, wood fragments and thin sand layers. Diatom analysis indicates that the deposit contains 5-8% polyhalobous (full marine) species, decreasing to 1-2% in the undisturbed lacustrine gyttja above. The tsunami event was dated to some time between 7300 and 6400 14 C yr BP. Lithostratigraphic profiles in the lake suggest that at least two large waves inundated the basin. The first and largest wave eroded most or all of the sediments previously deposited in the basin. The next wave caused minor erosion of the redeposited material. The waves deposited two generations of sand overlain by organic conglomerates, after which followed a unit of suspension material and normal lacustrine gyttja.     

Climate variability in West Greenland during the past 1500 years: evidence from a high‐resolution marine palynological record from Disko Bay

Ribeiro, S., Moros, M., Ellegaard, M. & Kuijpers, A. 2012 (January): Climate variability in West Greenland during the past 1500 years: evidence from a high‐resolution marine palynological record from Disko Bay. Boreas, Vol. 41, pp. 68–83. 10.1111/j.1502‐3885.2011.00216.x. ISSN 0300‐9483. Here we document late‐Holocene climate variability in West Greenland as inferred from a marine sediment record from the outer Disko Bay. Organic‐walled dinoflagellate cysts and other palynomorphs were used to reconstruct environmental changes in the area through the last c. 1500 years at 30–40 years resolution. Sea ice cover and primary productivity were identified as the two main factors driving dinoflagellate cyst community changes through time. Our data provide evidence for an opposite climate trend in West Greenland relative to the NE Atlantic region from c. AD 500 to 1050. For the same period, sea‐surface temperatures in Disko Bay are out‐of‐phase with Greenland ice‐core reconstructed temperatures and marine proxy data from South and East Greenland. This is probably governed by an NAO‐type pattern, which results in warmer sea‐surface conditions with less extensive sea ice in the area for the later part of the Dark Ages cold period (c. AD 500 to 750) and cooler conditions with extensive sea ice inferred for the first part of the Medieval Climate Anomaly (MCA) (c. AD 750 to 1050). After c. AD 1050, the marine climate in Disko Bay becomes in‐phase with trends described for the NE Atlantic, reflected in the warmer interval for the remainder of the MCA (c. AD 1050–1250), followed by cooling towards the onset of the Little Ice Age at c. AD 1400. The inferred scenario of climate deterioration and extensive sea ice is concomitant with the collapse of the Norse Western Settlement in Greenland at c. AD 1350.     

A stage 7 marine interglacial record (the Grødeland Interglacial) on Jaeren, southwestern Norway; foraminiferal, stable isotopes and amino acid evidence

Foraminiferal biostratigraphy, stable isotopes and amino-acid diagenesis have been investigated in a 125 m (+ 1 to — 124 m a.s.l.) long core from Jæren, southwestern Norway. Two marine units, the 42 m thick Grødeland Sand and the 8 m thick Sunde Sand, were found between till beds. Based on the biostratigraphic data, nine foraminiferal assemblage zones are defined. The Grødeland Sand shows a development from an ice-proximal glacial environment in the lower part, through an arctic, possibly shallow-water, environment, into a full interglacial open-shelf regime (the Grødeland Interglacial). The Grødeland Interglacial sediments (zone 6 Cassidulina laevigata-Cibicides zone) were deposited at a water depth of 20 m, in an open, high-energy shelf environment with temperature conditions similar to those prevailing in the northern North Sea today. The interglacial sediments are followed by deposits characteristic of an arctic environment which become more ice proximal upwards. Superimposed on the Grødeland Sand is a diamicton interpreted as till. Above the till is the upper marine unit (the Sunde Sand), which in the lower part yielded a shallow-water arctic fauna replaced upwards by an ice-proximal facies. The upper part of the Sunde Sand is barren of foraminifera and is superimposed by an upper till. The Sunde Interstadial is defined as a climatostratigraphic event resulting in deglaciation of western Norway and deposition of the Sunde Sand. Based on amino acid geochronology and inferences from the biostratigraphy, the Grødeland Interglacial is assigned to oxygen-isotope stage 7, whereas the Sunde Interstadial is assigned to the Early Weichselian. Combined with existing data from the North Sea region and the Norwegian Sea, it is concluded that for stage 7, in addition to stages 1 and 5e, there must have been a strong influx of Atlantic water into the Norwegian Sea north of the British Isles. This circulation created a similar north-south gradient in water masses in the North Sea to that which occurred during the Eemian and the Holocene. In the Nordic Seas, however, the stage 7 warm influx was probably restricted to the eastern part of the basin, unlike the later warm periods. This led to the development of fully interglacial conditions in the North Sea region, even though the palaeoceanographic data from the central part of the Nordic Seas suggest relatively cooler conditions for oxygen-isotope stage 7.     

Weathering of surface clasts as an indicator of the relative age of glacial deposits on Jameson Land, East Greenland

The relative age of glacial deposits on Jameson Land was investigated by weathering-based techniques. Two related methods, measurement of rind thickness and of Schmidt hammer rebound values. were added to a dating programme of luminescence-, amino acid- and ¹⁴C-analyses. Rind thicknesses differ significantly between areas which represent three glacial phascs, spanning a time interval from late Saale to Late Weichselian. Rebound values are more susceptible to external factors than the rind values but may, if these external factors are known, serve as a complement to the interpretation of rind development.     

DISTRIBUTED RAINFALL–RUNOFF MODEL INCORPORATING CHANNEL EXTENSION AND GRIDDED DIGITAL MAPS

Models based on gridded maps provide a simple and flexible way of modelling hydrological processes at the catchment scale. Such a model is described for humid temperate regions where no regional aquifer is present. The catchment is represented by a grid of 50 × 50 m interconnected cells. These are characterized by the depth and porosity of the soil layer, the slope and direction of drainage, the possible presence of a stretch of river and the presence or absence of forest canopy. Three types of hydrological processes are modelled: throughflow (described by a modified version of Darcy's law); channel flow (described by Manning's equation); and the interception–evaporation process as dependent on the presence or absence of forest canopy. The model predicts the hydrograph at the catchment outlet and the location of rivers in the catchment. These are compared with the observed river network, thus providing an additional means of assessing the model. © 1997 by John Wiley & Sons, Ltd.