Warm climate transitions: A general circulation modeling study of the Late Paleocene Thermal Maximum (∼56 Ma)

Abstract

Abstract. A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a-•100,000 year interval during which high-latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5øC over much of the continental interiors and precipitation over land increased by 5-10%. Nevertheless, despite specifying warm polar SSTs which exclude seaice; the model produces January continental interior temperatures less than -13øC, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind-driven ocean circulation response to model-produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8-28%. In general, our results are in agreement with deep-sea sediment-derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high-latitude hydrological cycle found in our LPTM experiment results raise important questions about high-latitude stable isotopic paleoclimate interpretations.

Productivity response of calcareous nannoplankton to Eocene Thermal Maximum 2 (ETM2)

“…Furthermore, extant coccolithophore assemblages in the Southwestern African margin, similar to other upwelling regions, are largely governed by changes in upwelling intensity (Boeckel and Baumann, 2004;Ziveri et al, 1995;Ziveri and Thunell, 2000). However, modeling studies are not conclusive about whether wind strength would have intensified during hyperthermal events (Huber and Sloan, 1999Sloan and Huber, 2001). While increased weathering is another mechanism that has been recognized as a potentially important source of nutrients to the ocean during the PETM (Bowen et al, 2004), a similar effect cannot be uniquely inferred from productivity patterns at our two locations during ETM2.…”

The Cenozoic climatic and topographic evolution of the western North American Cordillera

“…Moreover, regional climate models (RCM) for the early Paleogene Rocky Mountain region that account for high altitude mountains of the northern Rockies also suggest that a strong summer monsoon transported water vapor from the extensive Mississippi Embayment (Huber and Sloan, 1999;Sewall and Sloan, 2006). Our ␦…”

“…Unraveling the two competing effects is difficult even with this data-rich study of the western North American Cordillera. In fact, since the change of surface elevation affects both global and regional climate patterns (Kutzbach and others, 1989) and changing global climate can alter the global hydrologic cycle (Huber and Sloan, 1999) it is impossible to quantify changes in surface elevation from ␦…”

“…The following interpretation of this data set is guided by comparison of the modern (Kendall and Coplen, 2001;Dutton and others, 2005;Liu and others, 2010) and past (this study) maps of ␦ 18 O precipitation and results from GCM and RCM models of the paleoclimate of western North America (Huber and Sloan, 1999;Sewall and Sloan, 2006;Fricke and others, 2010;Poulsen and Jefferey, 2011).…”

The Paleocene-Eocene Thermal Maximum: Feedbacks Between Climate Change and Biogeochemical Cycles

“…Various climatemodeling studies have investigated the warming event at the Paleocene-Eocene boundary in response of the elevated greenhouse gas concentrations. These studies utilized atmospheric general circulation models (Sloan & Barron, 1992;Sloan & Rea, 1995;Huber & Sloan, 1999;Shellito et al, 2003;Shellito & Sloan, 2006), ocean general circulation models (Bice et al, 2000;Bice & Marotzke, 2002), or more recently coupled comprehensive climate models (Heinemann et al, 2009;Huber & Sloan, 2001;Huber & Caballero, 2003;Huber & Caballero, 2011;Lunt et al, 2010;Shellito et al, 2009;Winguth et al, 2010) to simulate the mean climate and its variability during the Eocene, but they have not been able to reproduce the high temperatures of the PETM in the high latitudes, and were controversial regarding the cause of this warming (Pagani et al, 2006b;Zeebe et al, 2009). Some of the more recent studies have investigated the climate feedbacks with a sequence of different greenhouse gas concentrations (e.g.…”