Past climate and the role of ocean heat transport: Model simulations for the Cretaceous

Patterns of surface current movements are interpreted for the Cretaceous in theCaribbean and Gulf of Mexico regions from a proxy paleobiologic database. Documented as generic presence/absence data points, the database was subjected to Monte Carlo simulations and 1,000 simulations were run per locality pair to generate indices of similarity among localities for the Aptian through Maastrichtian stages. Highsimilarity indices were interpreted to represent surface-current movements and inferred dispersal routes for planktotrophic larvae. Results were plotted on platetectonic reconstructions, and changes in water movements were charted through time. Clockwise rotation of surface currents was assumed for the Northern Hemisphere for the Cretaceous. West-to-north-to-eastward flow patterns were interpreted for Aptian through Cenomanian stages. These patterns were disrupted and surface flow was predominantly northward during the Turonian when sea level was at its highest Cretaceous peak. From the Coniacian through Maastrichtian, west-to-northto-east circulation patterns were reestablished. These westward, northward, and eastward surface flow patterns appear to be associated with rising, high, and falling sea level, but not with the peak Cretaceous sea level stand.

Section: Discussionmentioning

confidence: 99%

Evolution of Cretaceous surface current circulation patterns, Caribbean and Gulf of Mexico

Johnson¹

1999

“…Today, the oceans contribute approximately as much poleward heat transport as the atmosphere (Carissimo et al, 1985;Peixoto and Oort, 1992) and increased ocean heat transport has been cited as a means of maintaining low meridional thermal gradients during the Cretaceous (Barron, 1983(Barron, , 1987Covey and Barron, 1988;Crowley and North, 1991;Rind and Chandler, 1991;Barron et al, 1993b;Johnson et al, 1996). It has been estimated that oceanic heat transport increases of 50-70% are necessary to reproduce warm Mesozoic climates with low meridional thermal gradients (Rind and Chandler, 1991), primarily via a decreased sea ice/planetary albedo feedback.…”

Section: Late Cretaceous Ocean Heat Transport and Warm Continental Inmentioning

confidence: 98%

Late Cretaceous climate and vegetation interactions: Cold continental interior paradox

DeConto¹,

Hay²,

Thompson³

et al. 1999

Cretaceous climate has long been the focus of modeling studies, both for its unique nature and the need for understanding the fundamental climate processes and feedbacks during times of CO 2 induced "greenhouse" conditions. Prior simulations of Cretaceous climate using global climate models (GCMs) have not been successful in reproducing the low meridional thermal gradients and warm winter continental interior temperatures indicated by proxy climate data, forcing the equability of the Cretaceous to be questioned. Increased poleward ocean heat transport has been cited as a mechanism for maintaining low meridional thermal gradients during the Cretaceous. However, ocean heat transport values larger than the present day are difficult to reconcile with known physical oceanographic principles. In addition, low meridional thermal gradients suggest sluggish atmospheric circulation, implying that the advection of heat into the continental interiors would have been limited. Until recently, the effects of terrestrial ecosystems on pre-Quaternary climates have largely been ignored. Terrestrial ecosystems influence the global climate by affecting the exchange of energy, water, and momentum between the land surface and the atmosphere and provide an important boundary condition for pre-Quaternary climate simulations. Campanian (80 Ma) climate has been simulated using the GENESIS Version 2.0 Global Climate Model. To include the physical effects of vegetation on Campanian climate, a predictive Equilibrium Vegetation Ecology model (EVE) has been applied as a fully interactive component of the simulation. The coupled GENESIS-EVE model has reproduced the overall warmth, low meridional thermal gradients, and warm winter continental interiors characteristic of the Late Cretaceous. The simulated surface air temperatures, precipitation patterns, and predicted vegetation are well correlated with the geologic record at all latitudes. Late Cretaceous Antarctic and northern high latitude forests played an important role in the maintenance of low meridional thermal gradients, polar warmth, and equable continental interiors. Late Cretaceous forests decreased surface albedo, especially in the late winter and early spring prior to snow melt, and increased net radiation and latent heat flux. This contributed to tropospheric warming and increased

“…Results of climate model studies require that these reduced latitudinal thermal gradients must have reflected more intense latitudinal heat transport (Rind and Chandler, 1991;Barron et al, 1993Barron et al, , 1995. Sloan et al (1995) stated that the mechanism for the latitudinal transport of heat was likely a combination of oceanic and atmospheric processes with other factors such as high-latitude cloud cover.…”

Section: Late Cretaceous Latitudinal Surface Temperature Gradientsmentioning

confidence: 98%

Evolution of late Campanian-Maastrichtian marine climates and oceans

Barrera¹,

Savin²

1999

164

191

We present a global synthesis of the evolution of the climate/ocean system from the late Campanian at approximately 75 Ma to the end of the Maastrichtian at 65 Ma. This study is based on published and new oxygen and carbon isotope data of benthic and planktic foraminifera from a number of deep-sea sites, spanning the high to the low latitudes. Most of the sites were at depths that in the modern oceans are bathed by intermediate-water masses. The δ 18 O records of planktic and benthic foraminifera from most locations indicate that surface and intermediate waters cooled during the period 75 to 65.5 Ma, particularly at high latitudes. Model surface-water temperatures, based on δ 18 O values averaged for 1-m.y. intervals at each of the sites and corrected for the latitudinal variation of seawater δ 18 O using the present seawater latitudinal δ 18 O variation, indicate that the latitudinal thermal gradient increased from 10 to 13°C. Superimposed on the long-term trend there were two episodes during which, on a global scale, benthic foraminiferal δ 18 O values increased substantially, and then decreased. The first episode occurred between 71 and 69.5 Ma; the second began between 68 and 67.5 Ma, and terminated at about 65.5 Ma. During the first episode, the thermohaline circulation changed, and cool intermediate depth waters derived from high-latitude regions penetrated temporarily to the tropics, resulting in tropical Pacific intermediate waters becoming cooler than those in the high southern latitudes. Benthic foraminiferal δ 13 C values suggest that these cool waters may have been derived from high northern latitudes. The level of the carbonate compensation depth (CCD) shallowed substantially in the Pacific, Indian, and South Atlantic basins, although surface-water productivity may have increased during the time of altered thermohaline circulation. At the same time, the CCD deepened in the North Atlantic, where deep waters were warm and salty, and formed locally. From 67.5 to 65.5 Ma, intermediate waters in the southern high latitudes were cooler than those in other basins, indicating that the thermohaline circulation operated on a mode more similar to the present circulation. Both episodes of cooler intermediate water can be correlated with eustatic sea-level curves, suggesting that sea level was the most likely mechanism to change the circulation and/or source(s) of intermediate-deep waters. At 65.5 Ma, surface and intermediate waters warmed globally by about 3-4°C, and then cooled slightly at about 65.1 Ma. We suggest this increase in marine temperatures correlates with the timing of the main episode of Deccan Trap flood basalt eruptions and may have been caused by greenhouse global warming.