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51.
Aspects of open ocean deep convection variability are explored with a two-box model. In order to place the model in a region
of parameter space relevant to the real ocean, it is fitted to observational data from the Labrador Sea. A systematic fit
to OWS Bravo data allows us to determine the model parameters and to locate the position of the Labrador Sea on a stability
diagram. The model suggests that the Labrador Sea is in a bistable regime where winter convection can be either “on” or “off ”,
with both these possibilities being stable climate states. When shifting the surface buoyancy forcing slightly to warmer or
fresher conditions, the only steady solution is one without winter convection. We then introduce short-term variability by
adding a noise term to the surface temperature forcing, turning the box model into a stochastic climate model. The surface
forcing anomalies generated in this way induce jumps between the two model states. These state transitions occur on the interannual
to decadal time scale. Changing the average surface forcing towards more buoyant conditions lowers the frequency of convection.
However, convection becomes more frequent with stronger variability in the surface forcing. As part of the natural variability,
there is a non-negligible probability for decadal interruptions of convection. The results highlight the role of surface forcing
variability for the persistence of convection in the ocean. 相似文献
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Based on a well-established stratigraphic framework and 47 AMS-14C dated sediment cores, the distribution of facies types on the NW Iberian margin is analysed in response to the last deglacial sea-level rise, thus providing a case study on the sedimentary evolution of a high-energy, low-accumulation shelf system. 相似文献
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Kirsten Zickfeld Anders Levermann M. Granger Morgan Till Kuhlbrodt Stefan Rahmstorf David W. Keith 《Climatic change》2007,82(3-4):235-265
We present results from detailed interviews with 12 leading climate scientists about the possible effects of global climate
change on the Atlantic Meridional Overturning Circulation (AMOC). The elicitation sought to examine the range of opinions
within the climatic research community about the physical processes that determine the current strength of the AMOC, its future
evolution in a changing climate and the consequences of potential AMOC changes. Experts assign different relative importance
to physical processes which determine the present-day strength of the AMOC as well as to forcing factors which determine its
future evolution under climate change. Many processes and factors deemed important are assessed as poorly known and insufficiently
represented in state-of-the-art climate models. All experts anticipate a weakening of the AMOC under scenarios of increase
of greenhouse gas concentrations. Two experts expect a permanent collapse of the AMOC as the most likely response under a
4×CO2 scenario. Assuming a global mean temperature increase in the year 2100 of 4 K, eight experts assess the probability of triggering
an AMOC collapse as significantly different from zero, three of them as larger than 40%. Elicited consequences of AMOC reduction
include strong changes in temperature, precipitation distribution and sea level in the North Atlantic area. It is expected
that an appropriately designed research program, with emphasis on long-term observations and coupled climate modeling, would
contribute to substantially reduce uncertainty about the future evolution of the AMOC. 相似文献