Mark A. Chandler

Joint investigations of the middle Pliocene climate II: GISS GCM Northern Hemisphere results

Marine microfaunal data and terrestrial pollen records indicate that the middle Pliocene (ca. 3 Ma) climate is the most recent period in geologic history with global temperatures nearly as warm as those predicted for the coming century. We used the GISS GCM to examine the Pliocene climate by specifying sea surface temperatures and vegetation distributions derived from U.S.G.S. data sets. The simulation resulted in 1.4°C warming, annually averaged over the Northern Hemisphere. Warming was greatest at high latitudes; consequently, the equator to pole temperature gradient decreased by 11.5°C. Surface air temperature increases were greatest in winter, as decreased snow and sea ice triggered a positive albedo feedback effect. At low latitudes, temperatures were mostly unchanged except for an anomalous 3°C cooling over eastern Africa. This anomaly is supported by palynological data and, in the simulation, was a response to the weakening of the Hadley circulation, which used subtropical clouds and evapotranspiration rates to increase. Evaporation and precipitation rates decreased over the oceans and the appearance of negative P-E anomalies might implications for the Pliocene thermohaline circulation. The hydrological cycle intensified over the continents, where annual evaporation, rainfall, and soil moisture all increased. However, simulated summer drought conditions are not corroborated by terrestrial records, pointing to deficiencies in either the model, the boundary conditions, or the terrestrial data interpretations. n nThe Pliocene SST pattern implicates increased ocean heat flux as a component force behind the middle Pliocene warmth, since levels of CO2, large enough to cause the extreme high latitude temperatures, would generate more tropical warming than is indicated by floral and faunal records. Surface energy fluxes, calculated by the GCM, indicate that an increased meridional ocean heat flux of 32% could reproduce the data-derived SST distribution, despite weakened atmospheric transports. The decreased wind stress valuessuggest that any increase of ocean heat transports would probably have resulted from a strentthening of the thermohaline circulation.

Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes

Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period, ca 3.3–3.0u200aMa. Results indicate that, following a low stand of approximately 65u200am below present at marine isotope stage (MIS) M2 (ca 3.3u200aMa), sea level generally fluctuated by 20–30u200am above and below a mean value similar to present-day sea level. In addition to the low-stand event at MIS M2, significant low stands occurred at MIS KM2 (−40 m), G22 (−40u200am) and G16 (−60u200am). Six high stands of +10u200am or more above present day were also observed; four events (+10, +25,+15 and +30 m) from MIS M1 to KM3, a high stand of +15u200am at MIS K1, and a high stand of +25u200am at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice.

Middle Pliocene sea surface temperature variability

[1]xa0Estimates of sea surface temperature (SST) based upon foraminifer, diatom, and ostracod assemblages from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Ma. Pollen records and plant megafossils, although not as well dated, show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport are the leading candidates for the underlying cause of Pliocene global warmth. Despite being a period of global warmth, this interval encompasses considerable variability. Two new SST reconstructions are presented that are designed to provide a climatological error bar for warm peak phases of the Pliocene and to document the spatial distribution and magnitude of SST variability within the mid-Pliocene warm period. These data suggest long-term stability of low-latitude SST and document greater variability in regions of maximum warming.

Pliocene Role in Assessing Future Climate Impacts

Future warming projected by the Intergovernmental Panel on Climate Change (IPCC) has the potential to affect every person on Earth. Extreme weather events, rising sea level, and migrating ecosystems and resources may result in socioeconomic stresses. Although we can plan and prepare for what is expected, the most dangerous aspect of our changing climate is the uncertainty in climate sensitivity. n nTo reduce the uncertainties of climate change, paleoclimatologists are focusing on a possible yet imperfect analog to a future warmer climate.

Implications for the creation of warm saline deep water: Late Paleocene reconstructions and global climate model simulations

A global warming trend began during the late Paleocene that culminated in the early Eocene with the highest global temperatures of the Cenozoic. We have reconstructed late Paleocene surficial boundary conditions and modeled atmospheric conditions using the Goddard Institute for Space Studies general circulation model version II (GISS GCM II). These experiments were conducted to test the hypothesis that warm saline deep water formed during the late Paleocene and to understand atmospheric circulation near the beginning of a period of global warming. The warming is attributed primarily to increased sea surface temperatures at high latitudes. The sensitivity of the climate to ocean temperature was tested using two sea surface temperature distributions, each delimited latitudinally by oxygen isotope values, but with different east-west gradients. The simulations discussed here contain several features unique among warm climate experiments. The first experiment (P-1) used latitudinally constant (zonal) sea surface temperatures. The zonally distributed sea surface temperatures strengthen the general circulation of the atmosphere. In particular, Hadley Cell circulation is intensified, leading to extremes of precipitation in the equatorial region and extreme evaporation across subtropical oceans. The unusual results prompted a second experiment with modern east-west sea surface temperature gradients superimposed and referred to as P-Gradient (P-Grad). The east-west gradients in the sea surface temperature field exert a strong influence on the general atmospheric circulation, but the extreme zonality prevails. Under extreme zonal conditions it is possible to create a model where evaporation is in excess of precipitation by as much as 3 mm/day. If this occurred in restricted areas in a generally warmer ocean, such as the late Paleocene eastern Tethys Ocean and parts of the South Atlantic Ocean, it should be possible to create very saline water, which could become a component in warm saline deep water formation.

The Teaching of Anthropogenic Climate Change and Earth Science via Technology-Enabled Inquiry Education

ABSTRACT A gap has existed between the tools and processes of scientists working on anthropogenic global climate change (AGCC) and the technologies and curricula available to educators teaching the subject through student inquiry. Designing realistic scientific inquiry into AGCC poses a challenge because research on it relies on complex computer models, globally distributed data sets, and complex laboratory and data collection procedures. Here we examine efforts by the scientific community and educational researchers to design new curricula and technology that close this gap and impart robust AGCC and Earth Science understanding. We find technology-based teaching shows promise in promoting robust AGCC understandings if associated curricula address mitigating factors such as time constraints in incorporating technology and the need to support teachers implementing AGCC and Earth Science inquiry. We recommend the scientific community continue to collaborate with educational researchers to focus on developing those inquiry technologies and curricula that use realistic scientific processes from AGCC research and/or the methods for determining how human society should respond to global change.

GCM Hindcasts of SST Forced Climate Variability over Agriculturally Intensive Regions

The NASA/Goddard Institute for Space Studies (GISS) climatemodel is forced with globally observed sea-surfacetemperatures (SST) in five simulations, 1969–1991,with individual runs beginning from altered initialatmospheric conditions. The interannual variability ofmodeled anomalies of the Southern Oscillation Index,mid-tropospheric temperatures, 850 mb zonal winds andOutgoing Longwave Radiation over the tropical PacificOcean, which has the largest SST anomaly forcing, arestrongly correlated with observed trends which reflectENSO cycles. The models rainfall variability overthree agriculturally intensive regions, two tropicaland one mid-latitude, is investigated in order toevaluate the potential usefulness of GCM predictionsfor agricultural planning. The correct sign ofZimbabwe seasonal precipitation anomalies was hindcastwithin a useful range of consensus only for selectseasons corresponding to extreme ENSO events for whichanomalous circulation patterns were ratherrealistically simulated. The correlation betweenhindcasts of Nordeste monthly precipitation andobservations increases with time smoothing, reaching0.64 for 5-month running means. Consensus betweenindividual runs is directly proportional to theabsolute value of Niño3 SST so that during ElNiño and La Niña years most simulations agreeon the sign of predicted Nordeste rainfall anomalies.We show that during selected seasons the uppertropospheric divergent circulation and near surfacemeridional displacements of the ITCZ are realisticallyrepresented by the ensemble mean of the simulations.This realistic simulation of both the synopticmechanisms and the resulting precipitation changesincreases confidence in the GCMs potential forseasonal climate prediction.

Mid-Pliocene deep-sea bottom water temperatures based on ostracode Mg/Ca ratios, supplement to: Cronin, Thomas M; Dowsett, Harry J; Dwyer, Gary S; Baker, Paul A; Chandler, Mark A (2005): Mid-Pliocene deep-sea bottom-water temperatures based on ostracode Mg/Ca ratios. Marine Micropaleontology, 54(3-4), 249-261

We studied magnesium:calcium (Mg/Ca) ratios in shells of the deep-sea ostracode genus Krithe from a short interval in the middle Pliocene between 3.29 and 2.97 Ma using deep-sea drilling sites in the North and South Atlantic in order to estimate bottom water temperatures (BWT) during a period of climatic warmth. Results from DSDP and ODP Sites 552A, 610A, 607, 658A, 659A, 661A and 704 for the period Ma reveal both depth and latitudinal gradients of mean Mg/Ca values. Shallower sites (552A, 610A and 607) have higher mean Mg/Ca ratios (10.3, 9.7, 10.1 mmol/mol) than deeper sites (661A, 6.3 mmol/mol), and high latitude North Atlantic sites (552A, 610 and 607) have higher Mg/Ca ratios than low latitude (658A: 9.8 mmol/mol, 659A: 7.7 mmol/mol, 661A: 6.3 mmol/mol) and Southern Ocean (704: 8.0 mmol/mol) sites. Converting Mg/Ca ratios into estimated temperatures using the calibration of Dwyer et al. (1995) [Dwyer, G.S., Cronin, T.M., Baker, P.A., Raymo, M.E., Buzas, J.S., Correge, T., 1995. North Atlantic deepwater temperature change during late Pliocene and late Quaternary climatic cycles. Science 270, 1347–1351] suggests that mean middle Pliocene bottom water temperatures at the study sites in the deep Atlantic were about the same as modern temperatures. However, brief pulses of elevated BWT occurred several times between 3.29 and 2.97 Ma in both the North and South Atlantic Ocean suggesting short-term changes in deep ocean circulation.