Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Leavitt, S. W., Follett, R. F., Kimble, J. M., Pruessner, E. G. (2007). Radiocarbon andd13 C depth profiles of soil organic carbon in the U.S. Great Plains: A possible spatial record of paleoenvironment and paleovegetation. Quaternary International 162 (1): 21-34
ABSTRACT: Soil profiles from undisturbed grassland sites around the Great Plains of the USA were sampled for analysis of soil organic carbon (SOC) content (%), radiocarbon age and stable-carbon isotope composition (d13 C). With the exception of a few pronounced dating anomalies, SOC radiocarbon age generally increases steadily with depth back to 10–15,000 cal yr BP, the deepest soil intervals in 9 of the 12 sites. The radiocarbon ages were used to establish the chronology of changes in past plant distribution over time and space, based on SOCd13 C as an indicator of C3 and C4 plant abundance. Changes were referenced to an SOCd13 C value of−20‰, which is the approximate mid-point between C3 and C4 carbon isotope composition, i.e., an equal mixture of C3 and C4 carbon. Prior to 10,000 cal yr BP, the region was dominated by C3 plants with the exception of the southernmost Texas sites. From 10,000 to 2000 cal yr BP, C4 plants expanded their range, initially as a peninsula of C4-predominant grasses extending northeastward and ultimately dominating all but the northernmost border of the region. Finally, the C3-predominant region re-expanded after 1000 cal yr BP, perhaps as a response to the Little Ice Age cooling. Despite uncertainties associated with using radiocarbon-dated SOC-depth profiles as a proxy, the past C3 and C4 plant distribution inferred from SOCd13 C conforms well to results from other paleoclimate proxies, and differences may be helpful in targeting future research.
Bond, G., B. Kromer, J. Beer, R. Muscheler, M.N. Evans, W. Showers, S. Hoffman, R. Lotti-Bond, I. Hajdas, G. Bonane (2001). Persistent solar influence on North American climate during the Holocene. Science 294: 2130-2136
ABSTRACT: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
Benson, L., B. Linsley, J. Smoot, S. Mensing, S. Lund, S. Stine, A. Sarna-Wojcicki (2003). Influence of the Pacific Decadal Oscillation on the climate of the Sierra Nevada, California and Nevada. Quaternary Research 59 (2): 151-159
ABSTRACT: Mono Lake sediments have recorded five major oscillations in the hydrologic balance between A.D. 1700 and 1941. These oscillations can be correlated with tree-ring-based oscillations in Sierra Nevada snowpack. Comparison of a tree-ring-based reconstruction of the Pacific Decadal Oscillation (PDO) index  with a coral-based reconstruction of Subtropical South Pacific sea-surface temperature  indicates a high degree of correlation between the two records during the past 300 yr. This suggests that the PDO has been a pan-Pacific phenomena for at least the past few hundred years. Major oscillations in the hydrologic balance of the Sierra Nevada correspond to changes in the sign of the PDO with extreme droughts occurring during PDO maxima. Four droughts centered on A.D. 1710, 1770, 1850, and 1930 indicate PDO-related drought reoccurrence intervals ranging from 60 to 80 yr.
Thunell, R., E. Tappa, E. Kincaid, C. Pride (1999). Sea-surface temperature anomalies associated with the 1997–1998 El Niño recorded in the oxygen isotope composition of planktonic foraminifera. Geology 27 (9): 843-846
ABSTRACT: Anomalously warm sea-surface temperatures and associated high rainfall propagated northward from the eastern equatorial Pacific along the western margin of North America during the 1997–1998 El Niño. We present data from the Guaymas Basin (Gulf of California) and the Santa Barbara Basin (Southern California Borderlands) that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea-surface temperature changes related to the El Niño phenomenon. On the basis of this observation, the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past El Niño events.
ABSTRACT: The late Paleocene thermal maximum (LPTM) is associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle. We have developed a new orbital chronology for Ocean Drilling Program (ODP) Site 690 (Weddell Sea, Southern Ocean) by using spectral analysis of high-resolution geochemical records. The LPTM interval spans 11 precessional cycles yielding a duration of 210 to 220 k.y. Thed13 C anomaly associated with the LPTM has a magnitude of about -2.5‰ to -3‰; we show that about -2‰ of the excursion occurs within two steps that each were less than 1000 yr in duration. The remainder developed through a series of steps over 52 k.y. The timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates, punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial. Further, we are able to correlate the records between ODP Sites 690 and 1051 (western North Atlantic) on the scale of 21 k.y. cycles, which demonstrates that the details of thed13 C excursion are recognizable between distant sites. Comparison of cycle records at Sites 690 and 1051 suggests that sediment representing the interval 30 k.y. just prior to and at the onset of the LPTM are missing in the latter location. This unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k.y. of the start of the LPTM.
L. V. Benson, D.R. Currey, R. I. Dorn, K. R. Lajoie, C.G. Oviatt, S. W. Robinson, G. I. Smith, S. Stine (1990). Chronology of expansion and contraction of four Great Basin lake systems during the past 35,000 years. Paleogeography, Paleoclimatology, Paleoecology 78 (3-4): 241-286
ABSTRACT: During the past 35,000 years, Lake Bonneville, Lake Russell, and Lake Searles underwent a major period of lake-level change. The lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15,000 and 13,500 yr B.P. The rise of Lake Lahontan was gradual but not continuous, in part because of topographic constraints (intrabasin spill). Lake Lahontan also had an oscillation in lake level at 15,500 yr B.P. Radiocarbon-age estimations for materials that were deposited in the lake basins indicate that Lake Bonneville rose more or less gradually from 32,000 yr B.P., and had major oscillations in level between 23,000 and 21,000 yr B.P. and between 15,250 and 14,500 yr B.P. Lake Russell and Lake Searles had several major oscillations in lake level between 35,000 and 14,000 yr B.P. The timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states. All four lakes may have had nearly synchronous recessions between about 14,000 and 13,500 yr B.P. After the recessions, the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11,500 and 10,000 yr B.P. These data provide circumstantial evidence that the Younger Dryas Event affected climate on at least a hemispheric scale. During the Holocene, the four lakes remained at low levels, and small oscillations in lake level occurred. An important aspect of the lake-level data is the accompanying expansion of lake-surface area at the time of the last highstand. Lake Bonneville and Lake Lahontan had surface areas about 10 times larger than their mean-historical reconstructed areas whereas Lake Russell and Lake Searles had surface areas about 5 times larger than their mean-historical reconstructed areas. Differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream, or they may have resulted from lake/atmosphere feedback processes.
Benson, L.B., M. Kashgarian, R. Rye, S. Lund, F. Paillet, J. Smoot, C. Kester, S. Mensing, D. Meko, S. Lindström (2002). Holocene multidecadal and multicentennial droughts affecting northern California and Nevada. Quaternary Science Reviews 21 (4-6): 659-682
ABSTRACT: Continuous, high-resolutiond18 O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States. During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late–Holocene (3000–0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the meand18 O value of CaCO3 precipitated between 6500 and 3430 cal yr BP was 1.6‰ less than the mean value of CaCO3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in thed18 O baseline probably resulted from a transition to a wetter (>30%) and cooler (3–5°C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River–Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC andd18 O records from Owens Lake indicate that the first interval in the early Holocene (11,600–10,000 cal yr BP) was characterized by a drying trend that was interrupted by a brief (200 yr) wet oscillation centered at 10,300 cal yr BP. This was followed by a second early-Holocene interval (10,000–8000 cal yr BP) during which relatively wet conditions prevailed. During the early part of the middle Holocene (8000–6500 cal yr BP), high-amplitude oscillations in TIC in Owens Lake andd18 O in Pyramid Lake indicate the presence of shallow lakes in both basins. During the latter part of the middle Holocene (6500–3800 cal yr BP), drought conditions dominated, Owens Lake desiccated, and Lake Tahoe ceased spilling to the Truckee River, causing Pyramid Lake to decline. At the beginning of the late Holocene (~3000 cal yr BP), Lake Tahoe rose to its sill level and Pyramid Lake increased in volume.
ABSTRACT: Changes in solar constant over an 11 yr cycle suggest a certain, but limited, degree of solar forcing of climate. The high-resolution climate (oxygen isotope) record of the Greenland GISP2 (Greenland Ice Sheet Project 2) ice core has been analyzed for solar (and volcanic) influences. The atmospheric14 C record is used as a proxy of solar change and compared to the oxygen isotope profile in the GISP2 ice core. An annual oxygen isotope profile is derived from centimeter-scale isotope measurements available for the post-A.D. 818 interval. Associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium. The detailed record of volcanic aerosols, converted to optical depth and volcanic explosivity change, was also compared to the isotope record and the oxygen isotope response calibrated to short-term volcanic influences on climate. This calibration shows that century-scale volcanic modulation of the GISP2 oxygen isotope record can be neglected in our analysis of solar forcing. The timing, estimated order of temperature change, and phase lag of several maxima in14 C and minima in18 O are suggestive of a solar component to the forcing of Greenland climate over the current millennium. The fractional climate response of the cold interval associated with the Maunder sunspot minimum (and14 C maximum), as well as the Medieval Warm Period and Little Ice Age temperature trend of the past millennium, are compatible with solar climate forcing, with an order of magnitude of solar constant change of ~0.3%. Even though solar forcing of climate for the current millennium is a reasonable hypothesis, for the rest of the Holocene the century-scale events are more frequent in the oxygen isotope record than in the14 C record and a significant correlation is absent. For this interval, oceanic/atmospheric circulation forcing of climate may dominate. Solar forcing during the surprisingly strong 1470 yr climate cycle of the 11,000–75,000 yr B.P. interval is rather hypothetical.
ABSTRACT: It is hypothesised that the Medieval Warm Period was preceded and followed by periods of moraine deposition associated with glacier expansion. Improvements in the methodology of radiocarbon calibration make it possible to convert radiocarbon ages to calendar dates with greater precision than was previously possible. Dating of organic material closely associated with moraines in many montane regions has reached the point where it is possible to survey available information concerning the timing of the medieval warm period. The results suggest that it was a global event occurring between about 900 and 1250 A.D., possibly interrupted by a minor readvance of ice between about 1050 and 1150 A.D.
ABSTRACT: Chronological correlations established at different time scales among the lake-level fluctuations in the Jura and French Subalpine ranges, glacier movements in the Swiss and Austrian Alps, and the atmospheric14 C record during the last 7 millennia show coincidences between lake-level rises, glacier advances, and high14 C production and vice versa. These correspondences suggest that the short-term14 C variations may be an empirical indicator of Holocene palaeoclimates and argue for possible origins of Holocene climatic oscillations: (1) The varying solar activity refers to secular climatic oscillations and to major climatic deteriorations showing a ca. 2300-yr periodicity. (2) A question is raised about a relationship between the earth's magnetic field and climate. First, the weak-strength periods of the earth's dipole magnetic field (between 3800 and ca. 2500 B.C.) coincide with higher climate variability, and vice versa. Second, the ca. 2300-yr periods revealed by the14 C record and also by the major climatic deteriorations re. corded in Jurassian lakes (ca. 1500 A.D., ca. 800 B.C., and ca. 3500 B.C.) coincide with the ca. 2300-yr periods revealed by the earth's nondipole geomagnetic field. The present warming induced by anthropogenic factors should be intensified during the next few centuries by natural factors of climate evolution.
Baker, R.G., G. G. Fredlund, R. D. Mandel, E. A. BettisIII (2000). Holocene environments of the central Great Plains: multi-proxy evidence from alluvial sequences, southeastern Nebraska. Quaternary International 67 (1): 75-88
ABSTRACT: Pollen, plant macrofossils, phytoliths, carbon isotopes, and alluvial history from sediments exposed along the South Fork of the Big Nemaha River, southeastern Nebraska, USA, provide an integrated reconstruction of changes in Holocene vegetation, climate, and fluvial activity. From 9000 to 8500 uncalibrated14 C yr BP, climate became more arid and the floodplain and alluvial fans in the main valley aggraded rapidly, upland deciduous forest declined, and prairie attained its Holocene dominance. From 8500 to 5800 yr BP. upland forest elements disappeared, and even riparian trees were sparse under dry climatic conditions. Alluvial fans continued to aggrade but aggradation in the main valley was interrupted by a stable episode 7000 yr BP. From 5800 to 3100 yr BP, riparian forests returned to prominence, and droughts were intermittent. Alluviation was slower and punctuated by two major episodes of channel incision and terrace formation in the main valley. Aggradation on alluvial fans slowed and finally ceased near the end of this period. During a short dry interval from 3100 to 2700 yr BP riparian trees (except elm) disappeared, and prairie and weedy species became more abundant. This interval is represented by the organic Roberts Creek Member, and the alluvial setting was a slightly incised meandering channel belt. Habitats became similar to presettlement conditions during the last 2700 yr BP. Weedy taxa dominate modern samples, reflecting widespread disturbance. Alluvial fans and terrace surfaces were stable during the last 2500 years, but episodes of floodplain aggradation were punctuated by incision of the main channel.
ABSTRACT: Measured18 O/16 O ratios from the Greenland Ice Sheet Project 2 (GISP2) ice core extending back to 16,500 cal yr B.P. provide a continuous record of climate change since the last glaciation. High-resolution annual18 O/16 O results were obtained for most of the current millennium (A.D. 818-1985) and record the Medieval Warm Period, the Little Ice Age, and a distinct 11-yr18 O/16 O cycle. Volcanic aerosols depress central Greenland annual temperature (~1.5°C maximally) and annual18 O/16 O for about 4 yr after each major eruptive event. On a bidecadal to millennial time scale, the contribution of solar variability to Holocene Greenlandic temperature change is ~0.4°C. The role of thermohaline circulation change on climate, problematic during the Holocene, is more distinct for the 16,500-10,000 cal yr B.P. interval. (Analogous to14 C age calibration terminology, we express time in calibrated (cal) yr B.P. (A.D. 1950 = 0 cal yr B.P.)). The Oldest Dryas/Bølling/Older Dryas/Allerød/Younger Dryas sequence appears in great detail. Bidecadal variance in18 O/16 O, but not necessarily in temperature, is enhanced during the last phase of lateglacial time and the Younger Dryas interval, suggesting switches of air mass transport between jet stream branches. The branched system is nearly instantaneously replaced at the beginning of the Bølling and Holocene (at ~14,670 and ~11,650 cal yr B.P., respectively) by an atmospheric circulation system in which18 O/16 O and annual accumulation initially track each other closely. Thermodynamic considerations of the accumulation rate-temperature relationship can be used to evaluate the18 O/16 O-temperature relationship. The GISP2 ice-layer-count years of major GISP2 climate transitions also support the use of coral14 C ages for age calibration.
H. S. Godsey, D.R. Currey, M. A. Chan (2005). New evidence for an extended occupation of the Provo shoreline and implications for regional climate change, Pleistocene Lake Bonneville, Utah, USA. Quaternary Research 63 (2): 212-223
ABSTRACT: Lake Bonneville was a climatically sensitive, closed-basin lake that occupied the eastern Great Basin during the late Pleistocene. Ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the Bonneville basin and for facilitating correlations with regional and global records of climate change. Radiocarbon data from this and other studies suggest that the lake oscillated at or near the Provo level much longer than depicted by current models of lake level change. Radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed. These revisions to the Lake Bonneville hydrograph, coupled with independent evidence of climate change from vegetation and glacial records, have important implications for conditions in the Bonneville basin and during the Pleistocene to Holocene transition.
A. Cohen, M. Palacios-Fest, R. Negrini, P. Wigand, D. Erbes (2000). A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA: II. Sedimentology, paleontology and geochemistry. Journal of Paleolimnology 24 (2): 151-182
ABSTRACT: We have obtained a detailed paleoenvironmental record in the Summer Lake Basin, Oregon (northwestern Great Basin, US) spanning from 250 ka-5 ka. This record is derived from core and outcrop sites extending from a proximal deltaic setting to near the modern depocenter. Lithostratigraphic, paleontologic (ostracodes and pollen) and geochemical indicators all provide evidence for hydroclimate and climate change over the study interval. Lithostratigraphic analysis of the Summer Lake deposits allows subdivision into a series of unconformity - or paraconformity-bound lithosomes. The unconformity and facies histories indicate that the lake underwent several major lake-level excursions through the Middle and Late Pleistocene. High stands occurred between ~200 and ~165 ka, between ~89 and 50 ka and between ~25 and 13 ka. Uppermost Pleistocene and Holocene sediments have been removed by deflation of the basin, with the exception of a thin veneer of late Holocene sediment. These high stands correspond closely with Marine Oxygen Isotope Stages 6, 4 and 2, within the margin of error associated with the Summer Lake age model. A major unconformity from ~158 ka until ~102 ka (duration varies between sites) interrupts the record at both core and outcrop sites. Lake level fluctuations, in turn are closely linked with TOC and salinity fluctuations, such that periods of lake high stands correlate with periods of relatively low productivity, fresher water and increased water inflow/evaporation ratios. Paleotemperature estimates based on palynology and geochemistry (Mg/Ca ratios in ostracodes) indicate an overall decrease in temperature from ~236 ka-165 ka, with a brief interlude of warming and drying immediately after this (prior to the major unconformity). This temperature decrease was superimposed on higher frequency variations in temperature that are not evident in the sediments deposited during the past 100 ka. Indicators disagree about temperatures immediately following the unconformity (~102-95 ka), but most suggest warmer temperatures between ~100-89 ka, followed by a rapid and dramatic cooling event. Cooler conditions persisted throughout most of the remainder of the Pleistocene at Summer Lake, with the possible exception of brief warm intervals about 27-23 ka. Paleotemperature estimates for the proximal deltaic site are more erratic than for more distal sites, indicative of short term air temperature excursions that are buffered in deeper water. Estimates of paleotemperature from Mg/Ca ratios are generally in good agreement with evidence from upland palynology. However, there is a significant discordance between the upland pollen record and lake indicators with respect to paleoprecipitation for some parts of the record. Several possibilities may explain this discordance. We favor a direct link between lake level and salinity fluctuations and climate change, but we also recognize the possibility that some of these hydroclimate changes in the Summer Lake record may have resulted from episodic drainage captures of the Chewaucan River between the Summer Lake and Lake Abert basins.
G. J. Kukla, M. L. Bender, J. de Beaulieu, G. Bond, W. S. Broecker, P. Cleveringa, J. E. Gavin, T. D. Herbert, J. Imbrie, J. Jouzel, L. D. Keigwin, K. Knudsen, J. F. McManus, J. Merkt, D. R. Muhs, H. Müller, Ri. Z. Poore, S. C. Porter, G. Seret, N. J. Shackleton, C. Turner, P. C. Tzedakis, I. J. Winograd (2002). Last interglacial climates. Quaternary Research 58 (1): 2-13
ABSTRACT: The last interglacial, commonly understood as an interval with climate as warm or warmer than today, is represented by marine isotope stage (MIS) 5e, which is a proxy record of low global ice volume and high sea level. It is arbitrarily dated to begin at approximately 130,000 yr B.P. and end at 116,000 yr B.P. with the onset of the early glacial unit MIS 5d. The age of the stage is determined by correlation to uranium–thorium dates of raised coral reefs. The most detailed proxy record of interglacial climate is found in the Vostok ice core where the temperature reached current levels 132,000 yr ago and continued rising for another two millennia. Approximately 127,000 yr ago the Eemian mixed forests were established in Europe. They developed through a characteristic succession of tree species, probably surviving well into the early glacial stage in southern parts of Europe. After ca. 115,000 yr ago, open vegetation replaced forests in northwestern Europe and the proportion of conifers increased significantly farther south. Air temperature at Vostok dropped sharply. Pulses of cold water affected the northern North Atlantic already in late MIS 5e, but the central North Atlantic remained warm throughout most of MIS 5d. Model results show that the sea surface in the eastern tropical Pacific warmed when the ice grew and sea level dropped. The essentially interglacial conditions in southwestern Europe remained unaffected by ice buildup until late MIS 5d when the forests disappeared abruptly and cold water invaded the central North Atlantic ca. 107,000 yr ago.
ABSTRACT: We correlate oscillations in the hydrologic and/or cryologic balances of four Great Basin surface-water systems with Dansgaard–Oeschger (D–O) events 2–12. This correlation is relatively strong at the location of the magnetic signature used to link the lake records, but becomes less well constrained with distance/time from the signature. Comparison of proxy glacial and hydrologic records from Owens and Pyramid lakes indicates that Sierran glacial advances occurred during times of relative dryness. If our hypothesized correlation between the lake-based records and the GISP2d18 O record is correct, it suggests that North Atlantic D–O stades were associated with relatively cold and dry conditions and that interstades were associated with relatively warm and wet conditions throughout the Great Basin between 50,500 and 27,000 GISP2 yr B.P. The Great Basin lacustrine climate records reinforce the hypothesis that D–O events affected the climate throughout much of the Northern Hemisphere during marine isotope stages 2 and 3. However, the absolute phasing between lake-size and ice-cored18 O records remains difficult to determine.
D. Genty, D. Blamart, R. Ouahdi, M. Gilmour, A. Baker, J. Jouzel, S. Van-Exter (2003). Precise dating of Dansgaard–Oeschger climate oscillations in western Europe from stalagmite data. Nature 421 (6925): 833-837
ABSTRACT: The signature of Dansgaard–Oeschger events—millennial-scale abrupt climate oscillations during the last glacial period—is well established in ice cores and marine records. But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of14 C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using234 U/230 Th ratios. We find rapid climate oscillations coincident with the established Dansgaard–Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel, and deep-sea records, indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 ±0.6 and 67.4 ±0.9 kyr ago.
K. M. Menking, J. L. Bischoff, J. A. Fitzpatrick, J. W. Burdette, R. O. Rye (1997). Climatic/hydrologic oscillations since 155,000 yr B.P. at Owens Lake, California, reflected in abundance and stable isotope composition of sediment carbonate. Quaternary Research 48 (1): 58-68
ABSTRACT: Sediment grain size, carbonate content, and stable isotopes in 70-cm-long (~1500-yr) channel samples from Owens Lake core OL-92 record many oscillations representing climate change in the eastern Sierra Nevada region since 155,000 yr B.P. To first order, the records match well the marined18 O record. At Owens Lake, however, the last interglaciation appears to span the entire period from 120,000 to 50,000 yr B.P., according to our chronology, and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate. Sediment proxies reveal that the apparent timing of glacial–interglacial transitions, notably the penultimate one, is proxy-dependent. In the grain-size and carbonate-content records this transition is abrupt and occurs at ~120,000 yr B.P. In contrast, in the isotopic records the transition is gradual and occurs between 145,000 and 120,000 yr B.P. Differences in timing of the transition are attributed to variable responses by proxies to climate change.
N. G. Pisias, A. C. Mix, L. Heusser (2001). Millennial scale climate variability of the northeast Pacific Ocean and northwest North America based on radiolaria and pollen. Quaternary Science Reviews 20 (14): 1561-1576
ABSTRACT: Radiolaria and pollen abundances in marine sediment cores from the northeast Pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle (0–150 kyr). These data allow direct comparison of the climate response of continental and oceanic systems. Detailedd18 O and AMS-14 C measurements provide a link into global stratigraphic frameworks. Canonical correlation analysis extracts two modes of variation common to both the Radiolaria and pollen records. The first mode of variation correlates an assemblage of Radiolaria associated with coastal upwelling with increased redwood, western hemlock, and alder pollen. This association is consistent with the modern relationship between coastal upwelling, coastal fog and redwood forests. A second canonical mode relates an oceanic fauna now found in highest abundance in the far North Pacific with reduced pine and western hemlock pollen abundance.
Comparison of these records to an ice cored18 O record suggests that at wavelengths >3000 years, warm events in Greenland are correlated to intervals of increased coastal upwelling off Oregon, decreases in importance of very cold North Pacific fauna (suggesting warming), and increases in pollen associated with wetter coastal environments. Radiolarian based sea-surface temperature estimates suggest that the variability of the northeast Pacific on this time scale is about 2°C. Warming in the coastal regions reflects reduced advection of the California Current, but is moderated by increases in cool coastal upwelling. We infer that the response of the northeast Pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid- to high latitudes.
Preliminary analysis suggests that oceanic variability off Oregon at wavelengths <3000 years is similar to the Dansgaard–Oeschger cycles of the ice cored18 O records. This variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements. This finding suggests that, unlike longer-period millennial scale events, the propagation of the shorter wavelength events to the Northeast Pacific is through subtropical or tropical teleconnections.
ABSTRACT: New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming.10 Be data sets from the three areas were scaled to a single10 Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average10 Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this10 Be production rate yields ages comparable to those calculated with a commonly used36 Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions 16.836 Cl ka (Cosmogenic ages in this paper are labeled10 Be or36 Cl ka or just ka when both10 Be or36 Cl ages are being discussed; radiocarbon ages are labeled14 C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1s) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.510 Be ka at Pinedale, Wyoming, and between 16.3 and 17.336 Cl ka at Hogback Mountain, Colorado.
Cortese, G., A. Abelmann, R. Gersonde (2007). The last five glacial-interglacial transitions: A high-resolution 450,000-year record from the subantarctic Atlantic. Paleoceanography 22 (PA4203): doi:10.1029/2007PA001457
ABSTRACT: A submillennial resolution, radiolarian-based record of summer sea surface temperature (SST) documents the last five glacial to interglacial transitions at the subtropical front, southern Atlantic Ocean. Rapid fluctuations occur both during glacial and interglacial intervals, and sudden cooling episodes at glacial terminations are recurrent. Surface hydrography and global ice volume proxies from the same core suggest that summer SST increases prior to terminations lead global ice-volume decreases by 4.7 ± 3.7 ka (in the eccentricity band), 6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). A comparison between SST and benthicd13 C suggests a decoupling in the response of northern subantarctic surface, intermediate, and deep water masses to cold events in the North Atlantic. The matching features between our SST record and the one from core MD97-2120 (southwest Pacific) suggests that the super-regional expression of climatic events is substantially affected by a single climatic agent: the Subtropical Front, amplifier and vehicle for the transfer of climatic change. The direct correlation between warmerDTsite at Vostok and warmer SST at ODP Site 1089 suggests that warmer oceanic/atmospheric conditions imply a more southward placed frontal system, weaker gradients, and therefore stronger Agulhas input to the Atlantic Ocean.
L. V. Benson, S. P. Lund, J. W. Burdett, M. Kashgarian, T. P. Rose, J. P. Smoot, M. Schwartz (1998). Correlation of late-Pleistocene lake-level oscillations in Mono Lake, California, with North Atlantic climate events. Quaternary Research 49 (1): 1-10
ABSTRACT: Oxygen-18 (18 O) values of sediment from the Wilson Creek Formation, Mono Basin, California, indicate three scales of temporal variation (Dansgaard–Oeschger, Heinrich, and Milankovitch) in the hydrologic balance of Mono Lake between 35,400 and 12,90014 C yr B.P. During this interval, Mono Lake experienced four lowstands each lasting from 1000 to 2000 yr. The youngest lowstand, which occurred between 15,500 and 14,00014 C yr B.P., was nearly synchronous with a desiccation of Owens Lake, California. Paleomagnetic secular variation (PSV) data indicate that three of four persistent lowstands occurred at the same times as Heinrich events H1, H2, and H4.18 O data indicate the two highest lake levels occurred ~18,000 and ~13,10014 C yr B.P., corresponding to passages of the mean position of the polar jet stream over the Mono Basin. Extremely low values of total inorganic carbon between 26,000 and 14,00014 C yr B.P. indicate glacial activity, corresponding to a time when summer insolation was much reduced.
ABSTRACT: Decreased solar activity correlates with positive cosmogenic isotope anomalies, and with cool, wet climate in temperate regions of the world. The relationship of isotope anomalies to climate may be the opposite for areas influenced by monsoonal precipitation, i.e., negative anomalies may be wet and warm. Petersen (1988) has found evidence for increased summer precipitation in the American Southwest that can be shown to be coincident with negative14 C anomalies during the Medieval Warm Period. The present study compares palynological indicators of lake level for the Southwest with Petersen's data and with the14 C isotope chronology. Percentages of aquatic pollen and algae from three sites within the Arizona Monsoon record greater lake depth or fresher water from A.D. 700–1350, between the Roman IV and Wolf positive isotope anomalies, thereby supporting Petersens's findings. Maximum summer moisture coincides with maximum population density of prehistoric people of the Southwest. However, water depth at a more northern site was low at this time, suggesting a climate-isotope relationship similar to that of other temperate regions. Further analysis of latitudinal patterns is hampered by inadequate14 C dating.