Search

This study of Upper Pliensbachian – Bajocian/Bathonian deposits in a borehole drilled on the island of Anholt, Denmark incorporates sedimentology, biostratigraphy (palynomorphs and foraminifera),palaeomagnetism and coal petrology. The studied succession records a gradual change from marine inner shelf storm-influenced clays to mainly terrestrial sands, clays, and lignite containing a flora ofmainly freshwater algae and pollen. The regression was initiated at the Pliensbachian–Toarcian boundary and marine influence ceased during Bajocian–Bathonian times; the regression thus took place earlier at Anholt than in the centre of the Danish Basin. The sediments in the Anholt borehole are referred to the Fjerritslev and Haldager Sand Formations. Although the Lower–Middle Jurassicboundary is commonly placed at the boundary between the two formations, our data indicate that at Anholt the upper Fjerritslev Formation (member F-IV) is of Aalenian age. The Lower–Middle Jurassicboundary occurs close to the boundary between members F-III and F-IV of the Fjerritslev Formation.In contrast to other Lower–Middle Jurassic successions in the North Sea region, smectites of inferred volcanic origin are preserved in the Anholt section, suggesting limited burial and hence less intense diagenetic illitisation or chloritisation of smectites. A down-hole increase in diagenetic influence is reflected by the increase down-section both in the thermal stability of kaolinite and in the vitrinite reflectance. Kaolinite of inferred authigenic origin forms a white powder in the quartz-dominated sands of the Haldager Sand Formation; this kaolinite is thermally very unstable and is interpreted to be of late diagenetic, post-uplift origin. The vitrinite reflectance data indicate that the Jurassic formations have been exposed to thermal maturation corresponding to burial to a depth of 1000–1200 m below their present depth. Post-maturation uplift of the order of 1 km probably occurred partly during Late Cretaceous – Paleocene inversion in the Kattegat area and partly during Oligocene–Recent regional uplift, the latter being the most important of the two uplift phases. Palaeomagnetic data indicate that the main carrier of magnetic remanence is fine-grained magnetite. The stable remanence shows a pronounced inclination shallowing, which is attributed to post-depositional compaction.

This study reconstructs recent changes (1880–2017) in sea-ice conditions, using biomarkers (IP 25 and phytoplankton sterols) from three sediment cores located in a transect across Belgica Trough, on the Northeast Greenland continental shelf. These results are evaluated using instrumental and historical data from the same region and time period. Over the entire study period, IP 25 concentrations are highest at the inner shelf (site 90R) and decrease towards the mid-shelf (site 109R), with lowest values found at the outer shelf (site 134R). The PIP 25 index yields the highest sea-ice cover at sites 109R and 90R and the lowest at 134R, in agreement with observational records. A decline in sea-ice concentration, identified visually and using change-point analysis, occurs from 1971 in the observational sea-ice data at sites 90R and 109R. A change in sea-ice concentration occurs in 1984 at site 134R. Sea-ice conditions in these years aligns with an increase in sterol biomarkers and IP 25 at all three sites and a decline in the PIP 25 index at sites 90R and 134R. The outcomes of this study support the reliability of biomarkers for sea-ice reconstructions in this region. [ABSTRACT FROM AUTHOR]

This study reconstructs recent changes (ca. 120 years) in sea-ice cover, using biomarkers (IP25 and phytoplankton sterols) from three sediment cores located in a transect across Belgica Trough, on the Northeast Greenland continental shelf. These results are evaluated using instrumental and historical data from the same region and time period. Over the entire 120-year study period, IP25 concentrations are highest at the inner shelf (site 90R) and decrease towards the mid-shelf (site 109R), with lowest values found at the outer shelf (site 134R). The PIP25 index yields the highest sea-ice cover at sites 109R and 90R and lowest at 134R, in agreement with observational records. A decline in sea-ice cover, identified visually and using change point analysis, occurs from 1971 in the observational sea-ice data at sites 90R and 109R. A change in sea-ice cover occurs in 1984 at site 134R. Sea-ice cover in these years aligns with an increase in sterol biomarkers and IP25 at all three sites and decline in the PIP25 index at sites 90R and 134R. The outcomes of this study support the reliability of biomarkers for sea-ice reconstructions in this region. [ABSTRACT FROM AUTHOR]

The evolution of industrial-era warming across the continents and oceans provides a context for future climate change and is important for determining climate sensitivity and the processes that control regional warming. Here we use post-ad 1500 palaeoclimate records to show that sustained industrial-era warming of the tropical oceans first developed during the mid-nineteenth century and was nearly synchronous with Northern Hemisphere continental warming. The early onset of sustained, significant warming in palaeoclimate records and model simulations suggests that greenhouse forcing of industrial-era warming commenced as early as the mid-nineteenth century and included an enhanced equatorial ocean response mechanism. The development of Southern Hemisphere warming is delayed in reconstructions, but this apparent delay is not reproduced in climate simulations. Our findings imply that instrumental records are too short to comprehensively assess anthropogenic climate change and that, in some regions, about 180 years of industrial-era warming has already caused surface temperatures to emerge above pre-industrial values, even when taking natural variability into account., Author(s): Nerilie J. Abram (corresponding author) [1, 2]; Helen V. McGregor [3]; Jessica E. Tierney [4, 5]; Michael N. Evans [6]; Nicholas P. McKay [7]; Darrell S. Kaufman [7]; the [...]