Quantitative reconstruction of primary productivity in low latitudes during the last glacial maximum and the mid-to-late Holocene from a global Florisphaera profunda calibration dataset

The production of standardized relative sea-level (RSL) databases with a full consideration of uncertainty from many coastlines of the globe have enabled the exploration of RSL variability since the Last Glacial Maximum (LGM, 25 to 21 ka BP). Here, we expanded the global databases by evaluating 430 radiocarbon dated sea-level index points (SLIPs), which provided insights into the variability of RSL along the Atlantic African coast (Morocco to South Africa).Sea-level data were standardized following the International Geoscience Programme (IGCP) protocols to produce a suite of validated SLIPS as well as limiting points. The Atlantic African coast database was grouped in 21 regions according to geographical position and the distance from LGM ice-sheets. We applied a Gaussian model to estimate regional rates of RSL change and compared the regional data with the ICE-6G Glacial Isostatic Adjustment (GIA) model predictions.Our analysis indicates the RSL lowstand at the end of LGM was above -105 &#177; 4 m as indicated by a suite of marine limiting points. Since the LGM, RSL rose rapidly with average rates of up to 15 mm a-1 between 16 and 9 ka, notably in the Gulf of Guinea. The rates of RSL rise decrease to < 3 mm a-1 after ~7 ka BP. The mid-Holocene illustrates the emergence of a RSL high-stand which exceed the present mean sea-level between ~6.5 and ~4.5 ka BP. This high-stand is spatially variable and, in some regions was observed at elevations up to 2.5 m (e.g., Morocco, West Sahara, Congo, Namibia). In late Holocene RSL dropped gradually to the present datum. However, the coastal sector comprised between Senegal and Angola reveal late Holocene fluctuations, which are not reproduced by current GIA models. The Atlantic African coast database indicates RSL is controlled by the complex interplay by glacio-isostatic subsidence, rotational effects, ocean syphoning, continental levering, and 3-D variations in mantle viscosity structure as well as local forcing (e.g., compaction related subsidence). The Atlantic African coast database offers the possibility to better understand past RSL thereby providing constraints for more robust future sea-level projections of the west African coast in the framework of the on-going climatic change.

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Terrestrial Conditions at the Last Glacial Maximum and CLIMAP Sea-Surface Temperature Estimates: Are They Consistent?

Quaternary Research ◽

10.1016/0033-5894(85)90080-8 ◽

1985 ◽

Vol 24 (1) ◽

pp. 1-22 ◽

Cited By ~ 313

Author(s):

D. Rind ◽

D. Peteet

Keyword(s):

Last Glacial Maximum ◽

Glacial Maximum ◽

Sea Surface ◽

Radiation Balance ◽

Sea Surface Temperatures ◽

Last Glacial ◽

Surface Temperatures ◽

Low Latitudes ◽

The Last Glacial Maximum ◽

The Last Glacial

CLIMAP (1981, “Seasonal Reconstruction of the Earth's Surface at the Last Glacial Maximum,” Geological Society of America Map and Chart Series MC-36) boundary conditions were used as inputs to the GISS general circulation model, and the last glacial maximum (LGM) climate was simulated for six model years. The simulation was compared with snow line depression and pollen-inferred temperature data at low latitudes, specifically for Hawaii, Colombia, East Africa, and New Guinea. The model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence. An alternative experiment in which the CLIMAP sea-surface temperatures were uniformly lowered by 2°C produces a better fit to the land data although in Hawaii model temperatures are still too warm. The relatively warm CLIMAP tropical sea-surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model, in contrast to both evidence of LGM tropical aridity and the results of the experiment with colder ocean temperatures. With the CLIMAP sea-surface temperatures, the LGM global annual mean surface air temperature is 3.6°C colder than at present; if the ocean temperatures were allowed to cool in conformity with the model's radiation balance, the LGM simulation would be 5°–6°C colder than today, and in better agreement with the tropical land evidence.

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