ENHANCED LATENT HEAT TRANSPORT BY AN INTENSIFIED ALBIAN HYDROLOGIC CYCLE

 

Quantitative estimates of increased heat transfer by atmospheric H₂O vapor during the mid-Cretaceous greenhouse warming suggest that the intensified hydrologic cycle (modeled from sphaerosiderite proxy records) played a greater role in temperature buffering (cooling of the tropics and warming at high latitudes) than at present, and represents a viable alternative to oceanic heat transport. Precipitation-evaporation (P-E) balances define latitudinal zones with moisture deficits and moisture surpluses. Comparison of modeled Albian and modern P-E curves suggest amplification of the Albian moisture deficit between 7.5 and 30°N latitude (up to 65% greater), and amplified Albian moisture surplus in the mid to high latitudes (up to 45% greater). The tropical moisture deficit is calculated to represent an average heat loss of approximately 74 W/m² at 10°N paleolatitude (present 16.5 W/m²), and at 45°N an average heat gain of approximately 83 W/m² (present 23 W/m²); at 75°N an Albian heat gain of 19 W/m² is compared with present 4 W/m². These quantitative estimates of increased poleward heat transfer by H₂O vapor during the mid-Cretaceous greenhouse warming may help to explain the reduced equator-to-pole temperature gradients. The hydrologic cycle was modeled from the empirical paleolatitudinal trend in mid-Cretaceous meteoric sphaerosiderite d¹⁸O values of the Cretaceous Western Interior Basin (KWIB), which is steeper and lighter than the modern theoretical gradient. Sphaerosiderites are mm-scale FeCO₃ nodules found in wetland paleosols, and yield proxy records of mid-Cretaceous meteoric d¹⁸O values throughout North America (paleolatitudinal range: 34°N to 75°N). The trend in meteoric d¹⁸O values is the result of a more active hydrologic cycle with increased precipitation and evaporation rates during the mid-Cretaceous. The sphaerosiderite d¹⁸O values, empirical paleotemperature estimates, and modern meteoric d¹⁸O values were used to constrain a stable isotope mass balance model to quantify the Albian hydrologic cycle of the KWIB. The model was calibrated using modern d¹⁸O values, and the results suggest that mid-Cretaceous precipitation rates exceeded modern mid-high latitude rates (156-220% greater in mid latitudes [2600-3300 mm/yr], and 99% greater at high latitudes [550 mm/yr]).