Showing papers by "Wolfgang H Berger published in 2013"

On the Dynamics of The Ice Ages: Stage‐11 Paradox, Mid‐Brunhes Climate Shift, and 100‐Ky Cycle

Abstract: The Stage-11 Paradox consists in the fact that the stage sequence 12-11-10 has the greatest range of climatic variation in the Pleistocene, but only very modest forcing. The fundamental difference between the sequences 15-14-13 and 12-11-10 shows that the climate rules changed about 450,000 years ago. Basically, the world became more orderly and predictable. It marks the time when internal oscillation in the climate system became co-equal with Milankovitch forcing as a governing factor of ice-age dynamics. Thus, Stage 11 was so warm because Stage 12 was so cold. The maximum amplitude of climate variation around Stage 11 results from two opposing trends. One is an overall cooling trend, which when combined with changes in feedback mechanisms (NADW, albedo, carbon dioxide, marine-based ice) generates a propensity for ever-increasing glacial-interglacial amplitudes. The other is an overall negative feedback on glaciation, resulting from wearing down the base areas for ice-sheet buildup, which makes it more difficult to restart growing ice sheets after removal of ice, and makes it more difficult to build successive ice sheets to the same limit as previous ones. The combination of these factors is such that the system reached an opportunity for maximum contrast when forcing was at a minimum during mid-Brunhes time. On the whole, Stage 11 belongs with the succeeding interglacials, rather than the preceding ones. The new regime is characterized by strong terminations. An overall warming trend since 12-11-10 is nicely documented in the warm-water pool expansion in the western equatorial Pacific (which in turn stimulated reef growth).

The Nordic Seas: An Overview

Abstract: The aim of this overview paper is to provide a brief synthesis of the five review papers contained in the monograph. Prevailing south-westerly winds, oceanic flow patterns, and oceanic summer heat storage make the Nordic Seas region having temperatures 10 to 20 °C above the mean temperature at similar latitudes. The combination of the large heat import from south and the polar location implies that the region is prone to natural climate variations and particularly vulnerable for external forcings. Proxy data for the Holocene epoch indeed reveal large high-frequency climate fluctuations, as well as long-term variations spanning the ‘medieval warm period’ and the ‘little ice age’. In phase with a strengthening of the westerly winds since the 1960s, several oceanic key variables show trends unprecedented in available instrumental records, some of which extends back 50-100 years. State of the art climate models indicate that several of the changes may be linked to increased greenhouse gas forcing, and are therefore likely to be sustained or even amplified in the future. Furthermore, the marine cycling of carbon, and by that the major greenhouse gas carbon dioxide, is closely linked to the climate state of the region. The Nordic Seas region is, as one of few ocean locations, a sink for atmospheric carbon dioxide throughout the year. With the rapid developments in data acquisition, computational resources, and societal concerns for climate change and environmental issues, the review papers give an updated account of the present knowledge of the complex climate states of the Nordic Seas, and how the Nordic Seas influence the climate outside the region.