Department of the Interior U.S. Geological Survey Pliocene Climates: Scenario for Global Warming Abstracts from USGS Workshop, Denver, Colorado, October 23 - 25,1989 Edited by Linda B. Gosnell and Richard Z. Poore U.S. Geological Survey, Reston, VA 22092 Open-File Report 90-64 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Introduction: USGS Workshop on Pliocene Climates The US. Geological Survey (USGS) held a work­ tate quantitative estimates of environmental informa­ shop on Pliocene climates in Denver, Colorado on tion and the development of regional and global pat­ October 23-25,1989. The workshop brought together terns of climate data. members of the USGS who are working on a long- Better understanding of Pliocene climates, their ev­ term project to understand and map Pliocene cli­ olution, and rates and causes of change will provide mates and environments of the Northern Hemi­ important dues to future earth systems changes and sphere with interested collaborators from the USSR, impacts that will occur as a result of a greenhouse- The Geological Survey of Canada, the National Cen­ effect global warming. A major goal of the USGS Pli­ ter for Atmospheric Research, and the Institute for ocene Project is to produce a synoptic map or "snap­ Arctic and Alpine Research, University of Colorado. shot" of climate parameters during a time in the Plio­ Paleoclimate researchers from the USSR attended the cene representing conditions that are significantly workshop as part of an exchange and cooperative warmer than modern climates. The Pliocene "Scenar­ study of Pliocene climates that is organized under the io for Global Warming" will provide a means for test­ auspices of Working Group VIII of the US-USSR Bi­ ing and validating results of general circulation mod­ lateral Agreement on Protection of the Environment els (GCMs) which attempt to model global warming. The purposes of the workshop were to: 1) report Testing GCM results is crucial because these re­ and critique progress on individual research tasks sults are being used to predict future climate changes during fiscal year 1989 (FY 1989); 2) exchange infor­ due to increasing atmospheric concentrations of CC>2 mation and discuss methods for correlation, analysis and other greenhouse gasses. Important questions to and interpretation of proxy climate data, and data consider include: 1) are models capable of simulat­ management; 3) plan and prioritize the group's re­ ing warmer climates under different boundary condi­ search tasks for FY 1990; 4) continue dialogue with tions; 2) are regional responses to warming similar numerical climate modelers; and 5) expand efforts to for all warm intervals, regardless of the boundary involve the participation of researchers outside the conditions or the cause of warming; and 3) what was USGS who can contribute to the Pliocene climate re­ the impact of substantial global warming on the bio­ construction. sphere during the Pliocene? Answering these ques­ The USGS integrated study of Pliocene climates be­ tions will improve our ability to anticipate the effects gan in FY 1988 as a research objective of the USGS and consequences of future warming. Climate Change Program. During FY 1989, the USGS A great deal of progress towards achieving the ob­ Pliocene research project became an element of the jective of a Pliocene paleoclimatic reconstruction for USGS contribution to the U.S. Federal Global Change the Northern Hemisphere has been made as evi­ Research Program. denced by results summarized in the following con­ The Pliocene Epoch is of particular interest in cli­ tributions. For example, several techniques have mate history because Pliocene deposits record the been developed to estimate sea-surface temperatures transition from relatively warm global climates, and the temperatures of inner shelf waters of Plio­ when glaciers and sea ice were absent or greatly re­ cene seas. In addition, progress has been made in duced in the Northern Hemisphere, to the generally quantifying temperature and precipitation ranges in cooler climates of the Pleistocene with prominent terrestrial settings on the basis of fossil leaf assem­ high-frequency glacial-interglacial cycles and peren­ blages and in the dating and correlation of Pliocene nial ice-cover in the Arctic Ocean. Pliocene flora and localities in the critical Arctic basin. Important work fauna are very similar to modern flora and fauna, has begun on outlining the role of the carbon cycle in and Pliocene deposits are widespread and easily ac­ Pliocene climatic changes. cessible in both continental and marine settings. In The accompanying map shows the locations of the addition, most Pliocene sediments have undergone studies included in this report. A list of workshop little diagenetic alteration. All these attributes facili­ participants is in Appendix 1. Figure 1. General location of Pliocene research sites discussed in this volume Pliocene Environmental Changes At Tulelake, Siskiyou County, California, From 3 to 2 Ma David P. Adam, US. Geological Survey, Menlo Park CA 94025 J. Platt Bradbury, US. Geological Survey, Federal Center, Denver CO 80225 Hugh J. Rieck, US.Geological Survey, Flagstaff A2 86001 Diatoms and pollen grains deposited during the to 2.48 Ma; 219 to 229.68m depth). The low sedimen­ interval from 3 to 2 Ma at Tulelake, Siskiyou County, tation rate inferred from the paleomagnetic data is California, are well preserved, and their biostratigra- corroborated by the lithology of the section, which phy documents limnological and environmental shows a platy fracture pattern between 221 and 234m changes in this region. The entire 334m long sedi­ depth that is not present above or below that inter­ ment record is dated by paleomagnetic reversals and val. tephrochronology, and includes a continuous lacus­ Within the Pliocene, pine and TCT pollen show a trine stratigraphic record between 3 and 2 Ma. well-developed inverse relation, and the highest TCT Changes in the relative abundance of pine pollen vs. frequencies commonly exceed 50% (fig. 1). By con­ pollen of the Taxodiaceae, Cupressaceae and Taxa- trast, in the more recent part of the section the high­ ceae (TCD group reflect changes in the composition est TCT frequencies are significantly lower, and other of the regional forest through time; proportional pollen types, particularly Artemisia (sagebrush), be­ shifts between planktonic diatoms (Aulacoseira solida come more important. The strong inverse relation­ and large species of Stephanodiscus) and benthic dia­ ship between pine and TCT pollen evident in the Pli­ toms (FragUaria species) from the core can be inter­ ocene Tulelake deposits differs from the pattern at preted in terms of past changes in lake depth, open Tulelake during the past 1 Ma, but resembles pat­ water turbulence and seasonal thermal structure. terns observed at Hodgdon Ranch in the Sierra Neva­ These parameters are potentially under climatic con­ da (Adam, 1967; Latitude 38°N), and the cooler parts trol, and thereby may provide terrestrial paleodimat- of the pollen record from dear Lake, Lake County, ic insights for this time interval that can be compared California (Adam, 1988; latitude 39°N). We infer that with data from marine records. regional environmental conditions at Tulelake (lati­ The Tulelake Basin (lat. 41°57.27N, long. tude 42°N) between about 2 and 3 Ma resembled con­ 121°28.23'W, elev. 1229m), which is part of the Mo- ditions on the lower western slope of the Sierra today doc Plateau, is underlain by Tertiary and Quaternary and around Clear Lake during the cooler parts of the volcanic rocks broken by prominent normal faults last glacial cycle, rather than modern conditions near that strike mostly north and north-northwest. It is Tulelake. We interpret the pine and TCT curves in impounded by normal fault scarps to the west, by the terms of a model in which the ratio of TCT to pine Devils Garden and Medicine Lake volcanic fields to pollen increases with increasing temperature. Ac­ the southeast and south, by normal scarps to the east, cording to this model, a significant warm interval oc­ and by irregular highlands to the north. Both volcan- curred at Tulelake between about 2.8 and 2.6 Ma (fig. ism and tectonism are active in the region today. 1). The Pliocene deposits consist of interbedded lake Four major diatom zones characterize the Tule­ sediment and tephra. The lake sediment includes lake paleolimnological record between 3 and 2 Ma: a olive gray algal muds and marly units that are pri­ basal zone, (3.0 to 2.9 Ma), dominated by Stephanodis- marily massive but sometimes laminated, as well as cus, a lower intermediate zone, (2.9 to 2.65 Ma), char­ darker gray to black silts and clays. The chronology acterized by Aulacoseira solida (= Mdosira solida Eulen- for the Pliocene record is based on linear interpola­ stein), an upper intermediate zone, (2.65 to 2.4 Ma), tion between six paleomagnetic data points. The sedi­ with abundant FragQaria, and another A. solida zone, mentation rate established for the Gauss Normal- (2.4 to 2 Ma), that is interrupted by significant per­ Polarity Chron is in general agreement with rates ob­ centages of Cyclotdla bodanica between 215 and 210m served higher in the section, but sedimentation rates depth (estimated to date between 2.03 and 2.08 Ma). varied greatly during the interval from 2.0 to 25 Ma. Aulacoseira solida returns to dominance by 2.02 Ma, In particular, sedimentation was very slow near the but at the end of the Pliocene Fragilaria species be­ base of the Matuyama Reversed-Polarity Chron (2.12 come dominant once more. g-E. §1 I I I | I I I I §1 I I I | I I I I §11 I I | I I I I 8| I I I I I I I I §1 I I I | I I I I §| I I I j I I I I 3| I I I i i i|nii|iii^n^i Si 111111112i 1111111151111111113111111111 ^i 11111111 &! 1111111 i 11111111 §i 11111111 Si 11111111 §i 11111111 Si 11111111 i 1 Q Figure 1.