Climate Change and Earth-Ocean-Atmosphere Systems
Research: Palaeo-climatology, -oceanography and -limnology.
My research focuses on the generation of high-resolution paleoclimate records from marine and lacustrine sediments and, most recently, speleothems to better understand past climate dynamics. Field programs involve recovering sediment cores from selected lakes and ocean basins throughout the world and range from simple missions utilizing inflatable boats and hand-operated coring equipment to complex campaigns that utilize oceanic research vessels or lake drilling platforms. For the latter, I am actively involved the Integrated Ocean Drilling Program (IODP) and International Continental Drilling Program (ICDP). My research using deep-sea sediments has been concentrated geographically on the polar oceans of the North and South Atlantic, with the aim of integrating marine sediment and ice core records. The objective is to build marine sediment analogs to the polar ice cores in both the high-latitude North and South Atlantic and to study ocean-atmosphere linkages and the relative timing, phasing, and interhemispheric coupling mechanisms of climate change between the polar regions. My work using lake sediment cores and speleothems has mostly been centered in the circum-Caribbean region and especially Mesoamerica. The objective is to reconstruct Holocene climate change and, specifically, to explore how the ancient Maya affected their environment and, in turn, how environmental and climate change may have influenced their cultural evolution. New projects involving human-climate-environment interactions are being developed for the Khmer of Cambodia and Harappan civilization of the Indus Valley.
Current research projects include:
- Nature and origin of suborbital climate variability in the high-latitude North Atlantic during the Pleistocene
- The role of the Southern Ocean in global carbon cycling and climate change
- Climate change in the lowland Neotropics during the last glacial-to-interglacial cycle
- Human-climate-environment interactions
• Nature and origin of suborbital climate variability in the high-latitude North Atlantic during the Pleistocene
In the early 1990s, two observations in the North Atlantic region transformed the research agenda of the paleoclimate community. The discovery of flickering climatic oscillations in the Greenland ice cores, the so-called "Dansgaard-Oeschger" (D-O) events, demonstrated that large temperature changes had occurred over Greenland during the last glaciation. In 1992, Wally Broecker and colleagues proposed that layers of ice-rafted debris containing detrital carbonate (termed "Heinrich Events") in North Atlantic sediments were derived from massive discharge of ice from the Hudson Straits region. These observations spawned a proliferation of studies to document millennial-scale climate variability throughout the globe and determine its cause.
Beyond the last glacial cycle, our knowledge of millennial-scale variability relies on the marine record and is significantly reduced. Abrupt climate variability has been documented from older deep-sea sequences, but such studies have been limited by the availability of long cores with high sedimentation rates. To address this shortcoming, I participated in the planning and execution of IODP Expeditions 303 and 306. We recovered high sedimentation-rate sequences at several sites from the ice-rafted detritus (IRD) belt of the North Atlantic. The sites were chosen to yield long, complete, and continuous records of millennial-scale environmental variability (i.e., ice sheet-ocean interactions, deep circulation changes and sea surface conditions) for the Pleistocene. Core logging data measured during Exp. 303 provided clear evidence for millennial-scale climate variability occurring throughout the Pleistocene. Post-cruise research is focused on developing oxygen isotope stratigraphies for the sites and integrating them with geomagnetic paleointensity data, and using core logging and scanning XRF to extend the study of suborbital climate variability well beyond the last glacial cycle.
Hodell, D.A., and Curtis, J.H., 2008. Oxygen and carbon isotopes of detrital carbonate in North Atlantic Heinrich Events, Marine Geology, 256, 30-35, doi:10.1016/j.margeo.2008.09.010.
Hodell, D.A., Channell, J.E.T., Curtis, J., Romero, O., and Roehl, U., 2008. Onset of "Hudson Strait" Heinrich Events in the Eastern North Atlantic at the end of the Middle Pleistocene Transition (~640 ka)?, Paleoceanography, 23, doi:10.1029/2008PA001591.
Channell, J.E.T., Hodell, D.A., Xuan, C., Mazaud, A., and Stoner, J.S., 2008. A calibrated 1.5 Myr record of relative paleointensity from IODP Site U1308 (North Atlantic), Earth Planetary Science Letters, 274, 59-71.
Sierro, F.J., Hodell, D.A., Curtis, J., Flores, J.A., Reguera, I., Colmenero-Hidalgo, E., Barcena, M.A., Grimalt, J. and Canals, M., Impact of iceberg melting during Heinrich events on Mediterranean thermohaline circulation. Paleoceanography, 20:2, PA2019, 10.1029/2004PA001051.
• The role of the Southern Ocean in global carbon cycling and climate change
Over the last twenty years, paleoceanographers have recognized that processes occurring in the Southern Ocean have played a vital role in defining Earth's climate. For example, changes in Antarctic surface conditions and deep-water ventilation likely played an important role in controlling past changes in atmospheric CO2. Yet the amount of existing paleoceanographic data from the Southern Ocean is not nearly commensurate with the climatic importance of this region as a whole. Compared to the superb records available from the high-latitude North Atlantic, the Southern Ocean has relatively few deep-sea cores that are suitable for high-resolution paleoclimatic work. My research has specifically targeted areas of high sedimentation rates in the South Atlantic sector of the Southern Ocean. Research has thus far focused on generating continuous millennial-scale records of isotopic and sedimentologic changes for approximately the last half million years. Results have provided support for a physical cause of glacial-to-interglacial CO2 variation that involved Antarctic surface water processes (sea ice and surface stratification) and ventilation of deep water in the Southern Ocean, followed by a secondary response of the marine carbonate system.
Hodell, D.A., and Venz-Curtis, K.A., Late Neogene History of Deepwater Ventilation in the Southern Ocean, 2006. Geochemistry Geophysics Geosystems, 7, Q09001, doi:10.1029/2005GC001211.
Hodell, D.A., Venz, K.A., Charles, C.D., and Sierro, F.J., 2003a. The mid-Brunhes transition in ODP sites 1089 and 1090, In: A. W. Droxler, R. Z. Poore, and L. H. Burckle (eds.), Earth's Climate and Orbital Eccentricity: The Marine Isotope Stage 11 Question, AGU Geophysical Monograph Series, 137, pp. 113-129.
Hodell, D.A., Charles, C.D., Ninnemann, U.S., and Venz, K.A., 2003b. Pleistocene vertical carbon isotope gradients in the South Atlantic sector of the Southern Ocean, Geochemistry, Geophysics, Geosystems, 3(1), 10.1029/2002GC000367.
Hodell, D.A., Charles, C.D., and Sierro, F.J., 2001. Late Pleistocene evolution of the ocean's carbonate system, Earth Planetary Science Letters, 192, 109-124.
Mortyn, P.G., Charles, C.D., Ninnemann, U.S., Ludwig, K., and Hodell, D.A., 2003. Deep sea sedimentary analogs for the Vostok ice core, Geochemistry. Geophysics Geosystems, 4(8), 8405, DOI 10.1029/2002GC000475
• Climate change in the lowland Neotropics during the last glacial-to-interglacial cycle
Paleoclimatologists and modelers have increasingly focused on the tropics as a potentially important driver of global climate change because of the region's role in the Earth's energy budget and in regulating the water vapor content of the atmosphere. Tropical climate change is often expressed as variations in precipitation, as opposed to temperature changes that are more pronounced at higher latitudes. Tropical closed-basin lakes are sensitive recorders of changes in balance between precipitation and evaporation, and drilling technology now offers the opportunity to obtain long continuous sediment records from deep lake basins. Using the GLAD800 drilling platform (R/V Kerry Kelts), we recovered 1327 meters of continuous, high-quality sediment cores from Lake Peten-Itza, Guatemala. The overall objective is to decipher the history of the northern hemisphere Neotropical hydrologic cycle during the last glacial cycle, its relation to changes in the position of the Atlantic Intertropical Convergence Zone (ITCZ), and linkages to climate variability in the high-latitude North Atlantic. Marine-terrestrial linkages will be established by correlating rainfall/runoff proxies in sediment cores from Lake Peten-Itza with those from the nearby Cariaco Basin, northern Venezuela, to determine regional precipitation changes. In turn, the Peten-Itza record will be compared with proxy signals from the high latitudes of the North Atlantic to assess linkages with that region. The aim is to test our working hypothesis that past changes in lowland northern Neotropical precipitation were related to the meridional displacements in the mean position of the Atlantic ITCZ.
Hodell, D.A., Anselmetti, F.S., Ariztegui, D., Brenner, M., Curtis, J.H., Gilli, A., Grzesik, D.A., Guilderson, T.J., Muller, A.D., Bush, M.B., Correa-Metrio, Y.A., Escobar, J., and Kutterolf, S., 2008. An 85-ka Record of Climate Change in Lowland Central America, Quaternary Science Reviews, 27, 1152- 1165.
Hodell, D.A., Anselmetti, F., Brenner, M., Ariztegi, D., and the PISDP Scientific Party, The Lake Peten Itza Scientific Drilling Project, Scientific Drilling, 3, 25-29, doi:10.2204/iodp.sd.3.02.2006.
Anselmetti, F.S., Ariztegui, D., Hodell, D.A., Hillesheim, M.B, Brenner, M., Gilli, A., and McKenzie, J.A., 2006. Late Quaternary climate-induced lake level variations in Lake Peten-Itza, Guatemala., inferred from seismic stratigraphic analysis. Palaeogeogr. Palaeoclimatol. Palaeoecol., 230: 52-69.
• Human-climate-environment interactions
Our society is increasingly interested in the consequences of future climate and environmental change, as well as the role that humans play in these changes. Human civilizations throughout history have affected the environment and perhaps influenced climate through deforestation, agriculture, urbanization and industrialization. I have had a longstanding interest in how ancient civilizations affected their environment and, in turn, how environmental and climate change may have influenced cultural evolution. My work has been focused on the Maya region of Mesoamerica. One of the strongly held beliefs by Maya archaeologists was that climate in the region had remained relatively stable throughout the Holocene, and that major environmental perturbations were caused by human settlement and technology. My research has uncovered strong physical evidence for a series of droughts in the 9th and 10th century AD that coincided with the collapse of Classic Maya civilization. This finding has challenged archaeologists to reconsider the role that climate and environment may have played in Maya cultural evolution. In addition to climate change, my colleagues and I have demonstrated that early Maya inhabitants of the Yucatan Peninsula deforested the local landscape and caused dramatic increases in soil erosion, particularly in the watersheds of northern Guatemala during the Preclassic period. A protracted period of soil loss as a consequence of slash-and-burn agriculture and urbanization may have also contributed to the marked cultural transformations that occurred in the Terminal Classic Period.
My most recent research effort is concerned with testing the Terminal Classic drought hypothesis using speleothem paleoclimatology. Speleothems hold much promise for reconstructing past climate on the Yucatan Peninsula and assessing its impact on the ancient Maya civilization because: 1) The Yucatan Peninsula is a karst platform with abundant cave systems. 2) With appropriately chosen records, the 18O of speleothem calcite mainly reflects variations in the 18O of precipitation that, in turn, is highly correlated with rainfall amount. 3) Uranium disequilibrium series (i.e., U/Th) offers an accurate radiometric method to date speleothems; and 4.) Speleothem growth rates are high enough to resolve climate changes on timescales less than a decade (i.e., less than a human lifetime). This research will test climatic inferences derived previously from our studies of lake sediment cores in the region and will aid archaeologists to assess the role that climate change may have played in cultural transformation.
Yaeger, J., and Hodell, D.A., 2008. Climate-culture-environment interactions and the collapse of Classic Maya civilization. In: D.H. Sandweiss and J. Quilter (Eds.), El Nino, Catastrophism, and Culture Change in Ancient America, Dumbarton Oaks, pp. 187-242.
Mueller, A.D., Islebe, G.A., Hillesheim, M.B., Grzesik, D.A., Anselmetti, F.S., Ariztegui, D., Brenner, M., Curtis, J.H., Hodell, D.A., and Venz, K.A., 2008. Climate drying and associated forest decline in the lowlands of northern Guatemala during the late Holocene, Quaternary Research, doi:10.1016/j.yqres.2008.10.002
Hodell, D.A., Brenner, M., and Curtis, J.H., 2007. Climate and Cultural History of the northeastern Yucatan Peninsula, Quintana Roo, Mexico, Climatic Change, DOI 10.1007/s10584-006-9177-4
Anselmetti, F.S., Hodell, D.A., Ariztegui, D., Brenner, M., and Rosenmeier, M.F., 2007. Quantification of soil erosion rates related to ancient Maya deforestation. Geology, 35(10), 915-918.
Hodell, D.A., Brenner, M., and Curtis, J.H. 2005. Terminal Classic drought in the northern Maya Lowlands inferred from multiple sediment cores in Lake Chichancanab (Mexico). Quaternary Science Reviews, 24: 1413-1427.
Hodell, D.A., Brenner, M., Curtis, J.H., Medina-Gonzalez, R., Rosenmeier, M.F., Guilderson, T.P., Chan-Can, E.I. and Albornaz-Pat , A., 2005. Climate change on the Yucatan Peninsula during the Little Ice Age. Quaternary Research 63:109-121.
Hodell, D.A., Brenner, M., Curtis, J.H., and Guilderson, T., 2001. Solar forcing of drought frequency in the Maya lowlands, Science, 292, 1367-1369.
Hodell, D.A., J.H. Curtis, and M. Brenner, 1995, Possible role of climate in the collapse of Classic Maya civilization, Nature, 375, 391-394.
Older Publications by Professor David Hodell