Erik Thomsen
Aarhus University, Geoscience, Faculty Member
The use of strontium isotopes in pre-historic mobility studies requires accurate isoscapes for evaluating whether pre-historic individuals are local to the areas in which they were buried or not. Isoscapes are often based on modern-day... more
The use of strontium isotopes in pre-historic mobility studies requires accurate isoscapes for evaluating whether pre-historic individuals are local to the areas in which they were buried or not. Isoscapes are often based on modern-day samples, commonly surface waters. There is, however, growing evidence that modern-day farming has a significant impact on the strontium isotopic composition of surface waters and farmed soils, mainly due to the use of agricultural lime for soil improvement. In this paper, we investigate the fate of strontium from agricultural lime in an experimentally-manipulated field in central Jutland, Denmark. Agricultural limestone was added to this field at very high rates in 2012 and 2013 to investigate CO2 storage in soils. Strontium was first measured from the site in 2014. In 2019 we reevaluated strontium concentrations and found that 80–100% of the strontium from the agricultural lime had leached out of the organic-rich topsoil, and likely seeped into the u...
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A high-resolution piston core, ENAM93-21, from a water depth of 1020 m near the Faeroe-Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice-rafted... more
A high-resolution piston core, ENAM93-21, from a water depth of 1020 m near the Faeroe-Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice-rafted detritus (IRD), and distribution of planktonic and benthic foraminifera. The core, covering the last 58,000 years, is correlated with the Greenland ice cores and compared with paleorecords from the Norwegian Sea and the North Atlantic Ocean. All fifteen Dansgaard-Oeschger climatic cycles recognized from the investigated time period in the Greenland ice cores have been identified in the ENAM93-21 core. Each cycle is subdivided into three intervals on the basis of characteristic benthic and planktonic faunas. Interstadial intervals contain a relatively warm planktonic fauna and a benthic fauna similar to the modern fauna in the Norwegian Sea. This indicates thermohaline convection as at present, with a significant contribution of deep water to the North Atlantic Deep Water (NADW). Transitional cooling intervals are characterized by more cold water planktonic foraminfera and ice-related benthic species. The benthic fauna signifies restricted bottom water conditions and a reduced contribution to the NADW. The peak abundance of N. pachyderma (s.) and the coldest surface water conditions are found in the stadial intervals. The benthic fauna is dominated by species with an association to Atlantic Intermediate Water, suggesting an increased Atlantic influence in the Norwegian Sea, and there was probably no contribution to the NADW through the Faeroe-Shetland Channel. The three different modes of circulation can be correlated to paleoceanographic events in the Norwegian Sea and the North Atlantic Ocean.
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A number of short-lasting warm periods (interstadials) interrupted the otherwise cold climate of the last glacial period. These events are supposedly linked to the inflow of the warm Atlantic surface water to the Nordic seas. However,... more
A number of short-lasting warm periods (interstadials) interrupted the otherwise cold climate of the last glacial period. These events are supposedly linked to the inflow of the warm Atlantic surface water to the Nordic seas. However, previous investigations of planktonic foraminifera from the Nordic seas have not been able to resolve any significant difference between the interstadials and intervening cold stadials, as the faunas are continuously dominated by the polar species Neogloboquadrina pachyderma s. Here we examine the planktonic foraminifera assemblages from a high-resolution core, LINK17, taken at 1500 m water depth off northern Scotland below the warmest part of the inflowing Atlantic water. The core comprises the time period 34–10 calibrated ka B.P., the coldest period of the last glaciation and the deglaciation. The results reveal a hitherto unknown faunistic variability indicating significant fluctuations in both surface water inflow and in summer sea surface temperatures. During the interstadials, relatively warm Atlantic surface water (4–7°C) flowed north into the eastern Norwegian Sea. During the stadials and Heinrich events the surface inflow stopped and the temperatures in the study area dropped to <2°C. The Last Glacial Maximum was nearly as warm as the interstadials, but the inflow was much more unstable. The data reveal two previously unrecognized warming events each lasting more than 1600 years and preceding Heinrich events HE3 and HE2, respectively. By destabilizing the ice sheets on the shelves the warmings may have played a crucial role for the development of Heinrich events HE2 and HE3.
Research Interests: Geology and Sediment Core
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A high-resolution piston core, ENAM93-21, from a water depth of 1020 m near the Faeroe-Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice-rafted... more
A high-resolution piston core, ENAM93-21, from a water depth of 1020 m near the Faeroe-Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice-rafted detritus (IRD), and distribution of planktonic and benthic foraminifera. The core, covering the last 58,000 years, is correlated with the Greenland ice cores and compared with paleorecords from the Norwegian Sea and the North Atlantic Ocean. All fifteen Dansgaard-Oeschger climatic cycles recognized from the investigated time period in the Greenland ice cores have been identified in the ENAM93-21 core. Each cycle is subdivided into three intervals on the basis of characteristic benthic and planktonic faunas. Interstadial intervals contain a relatively warm planktonic fauna and a benthic fauna similar to the modern fauna in the Norwegian Sea. This indicates thermohaline convection as at present, with a significant contribution of deep water to the North Atlantic Deep Water (NADW). Transitional cooling intervals are characterized by more cold water planktonic foraminfera and ice-related benthic species. The benthic fauna signifies restricted bottom water conditions and a reduced contribution to the NADW. The peak abundance of N. pachyderma (s.) and the coldest surface water conditions are found in the stadial intervals. The benthic fauna is dominated by species with an association to Atlantic Intermediate Water, suggesting an increased Atlantic influence in the Norwegian Sea, and there was probably no contribution to the NADW through the Faeroe-Shetland Channel. The three different modes of circulation can be correlated to paleoceanographic events in the Norwegian Sea and the North Atlantic Ocean.
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Increasingly, strontium (Sr) isotopes are used to distinguish locals and migrants in prehistoric studies, by measuring87Sr/86Sr in human remains and comparing these values to the distribution of the bioavailable87Sr/86Sr in the study... more
Increasingly, strontium (Sr) isotopes are used to distinguish locals and migrants in prehistoric studies, by measuring87Sr/86Sr in human remains and comparing these values to the distribution of the bioavailable87Sr/86Sr in the study area, often in surface water. However, it has recently been shown that agricultural lime can have a substantial impact on the87Sr/86Sr ratio and strontium concentration in surface water in areas where soils are low- to non-calcareous. Agricultural lime is rich in strontium with low87Sr/86Sr ratios, such that interpretations of prehistoric migration based on surface waters affected by agricultural lime often overestimate the number of migrants in a given area. However, the impact of agricultural lime was questioned in a new study, which argues that strontium derived from agricultural lime is retained in the topsoil of the fields and therefore do not contaminate the surface water. In the present study and in a companion study in this volume, we show that ...
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Agricultural liming severely affects the use of strontium isotopes in prehistoric provenance and migration studies.
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Foraminiferal responses to upwelling variations in the South China Sea over the last 220000 years B. Huang, Z. Jian, X. Cheng and P. Wang...................................................... 1 Age and paleoenvironment of the Maastrichtian to Paleocene of the Mahajanga Basin, Madagascar: a multid...more
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Thirteen piston and gravity cores from the Faroe–Shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions. Eight time-slices between 18 ka BP and the present were reconstructed to... more
Thirteen piston and gravity cores from the Faroe–Shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions. Eight time-slices between 18 ka BP and the present were reconstructed to study variations in surface and deep water exchange between the SE Norwegian Sea and the northeast Atlantic Ocean. Today, a relatively strong northward flow of warm North
Research Interests: Earth Sciences, Geology, Marine Geology, North Atlantic Ocean, North Atlantic, and 14 moreForaminifera, Thermohaline Circulation, Surface Water, Younger Dryas, Last Glacial Maximum, Oxygen Isotope, Deep water, Early Holocene, Shetland, Water Flow, Water Masses, Late Quaternary, Northeast Atlantic, and Climatic condition
The {delta} 18 O and {delta} 13 C values of benthic foraminifera from the cold stadials of the last glacial period in the Nordic seas are low, whereas the values from the warm interstadials are high. The low values have been attributed to... more
The {delta} 18 O and {delta} 13 C values of benthic foraminifera from the cold stadials of the last glacial period in the Nordic seas are low, whereas the values from the warm interstadials are high. The low values have been attributed to brine formation carrying a ...
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The Danian-Selandian boundary at Svejstrup is characterized by an abrupt facies change from a pure limestone to a terrigeneous marl. The top of the Danian limestone is an intensively burrowed abrasion surface. The Sel:indian deposits... more
The Danian-Selandian boundary at Svejstrup is characterized by an abrupt facies change from a pure limestone to a terrigeneous marl. The top of the Danian limestone is an intensively burrowed abrasion surface. The Sel:indian deposits are initiated by a conglomerate of glauconitized and phosphatized limestone pebbles. Although the boundary at Svejstrup is very similar to the nearby section at Hvalklse, the time interval included in the hiatus at Svejstrup is greater than at Hvall0se. The coccoliths and dinoflagellates indicate different ages for the top of the Danian. It is also shown that the Danian sequences in the Harre and the Viborg 1 borings include strata younger than in any previously described Danian sections. At both of these localities a number of coccoliths and a dinoflagellate, Spinidinium densispinatum, hitherto only recorded from the Selandian, occur in the Danian limestone. The top of the Danian at Harre and Viborg 1 is of upper NP4 or lower NP5 age. The calcareo...
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Abstract Piston core LINK14 from 346 m water depth on the eastern shelf of the Faroe Islands in the Faroe-Shetland Channel has been investigated in order to reconstruct temperature and salinity changes of the Atlantic surface Water during... more
Abstract Piston core LINK14 from 346 m water depth on the eastern shelf of the Faroe Islands in the Faroe-Shetland Channel has been investigated in order to reconstruct temperature and salinity changes of the Atlantic surface Water during the Holocene. We ...
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The precise reason for the differences and out-of-phase relationship between the abrupt Dansgaard-Oeschger warmings in the Nordic seas and Greenland ice cores and the gradual warmings in the south-central Atlantic and Antarctic ice cores... more
The precise reason for the differences and out-of-phase relationship between the abrupt Dansgaard-Oeschger warmings in the Nordic seas and Greenland ice cores and the gradual warmings in the south-central Atlantic and Antarctic ice cores is poorly understood. Termed the bipolar seesaw, the differences are apparently linked to perturbations in the ocean circulation pattern. Here we show that surface and intermediate-depth water south of Iceland warmed gradually synchronously with the Antarctic warming and out of phase with the abrupt warming of the Nordic seas and over Greenland. The hinge line between areas showing abrupt and gradual warming was close to the Greenland-Scotland Ridge and the marine system appears to be a 'push-and-pull' system rather than a seesaw system. 'Pull' during the warm interstadials, when convection in the Nordic seas was active; 'push' during the cold stadials, when convection stopped and warm water from the south-central Atlantic pu...
This paper demonstrates the fabrication, characterization, and experimental imaging results of a 62+62 element λ/2-pitch row-column-addressed capacitive micromachined ultrasonic transducer (CMUT) array with integrated apodization. A new... more
This paper demonstrates the fabrication, characterization, and experimental imaging results of a 62+62 element λ/2-pitch row-column-addressed capacitive micromachined ultrasonic transducer (CMUT) array with integrated apodization. A new fabrication process was used to manufacture a 26.3 mm by 26.3 mm array using five lithography steps. The array includes an integrated apodization, presented in detail in Part I of this paper, which is designed to reduce the amplitude of the ghost echoes that are otherwise prominent for row-column-addressed arrays. Custom front-end electronics were produced with the capability of transmitting and receiving on all elements, and the option of disabling the integrated apodization. The center frequency and -6-dB fractional bandwidth of the array elements were 2.77 ± 0.26 MHz and 102 ± 10%, respectively. The surface transmit pressure at 2.5 MHz was 590 ± 73 kPa, and the sensitivity was 0.299 ± 0.090 V/Pa. The nearest neighbor crosstalk level was -23.9 ± 3....