PRECIPITATION RATES AND ATMOSPHERIC HEAT TRANSPORT DURING THE CENOMANIAN GREENHOUSE WARMING IN NORTH AMERICA

Stable isotope mass balance modeling of meteoric δ¹⁸O values from the Cenomanian Stage of the Cretaceous Western Interior Basin (KWIB) suggest that precipitation and evaporation fluxes were greater than that of the present and significantly different from simulations of Albian KWIB paleohydrology. Sphaerosiderite meteoric δ¹⁸O values have been compiled from the Lower Tuscaloosa Formation of southwestern Mississippi, The Dakota Formation, Fairbury Nebraska, and the Dunvegan Formation of British Columbia. These paleosol siderite δ¹⁸O values define a paleolatitudinal gradient ranging from -4.2 ‰ VPDB at 25°N to -12.5‰ VPDB at 55°N. This trend is significantly steeper and more depleted than a modern theoretical siderite gradient (25°N: -1.7 ‰ ; 65°N: -5.6 ‰ VPDB ), and a Holocene meteoric calcite trend (27°N: -3.6 ‰ ; 67°N: -7.4 ‰ VPDB). The Cenomanian gradient is also steeper than the Albian trend determined for the KWIB. A stable-isotope mass balance model has been used to generate estimates of precipitation and evaporation fluxes and precipitation rates. Estimates of Cenomanian precipitation rates in the KWIB range from 1500 mm/yr at 25°N paleolatitude to 3100 mm/yr at 45°N paleolatitude. The precipitation-evaporation (P-E) flux values were used to delineate zones of moisture surplus and moisture deficit. Comparisons between Cenomanian P-E and modern latitudinal trends shows an amplification of low-latitude moisture deficits between 5-25°N paleolatitude and moisture surpluses between 40-60°N paleolatitude. The low latitude moisture deficits correlate with a mean annual average heat loss of 71 W/m2 at 10°N paleolatitude (present, 16 W/m2). The increased precipitation flux and moisture surplus in the mid-latitudes corresponds to a mean average annual heat gain of 160 W/m2 at 50°N paleolatitude (present, 21 W/m2). The Cenomanian low latitude moisture deficit is similar to that of the Albian, however the mid-latitude (40-60°N) precipitation flux values and precipitation rates are significantly higher (Albian: 2250 mm/yr at 55°N; Cenomanian: 3100 mm/yr at 45°N). The heat transferred to the atmosphere via latent heat of condensation was almost 7.6 x that of the present at 50°N.