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What's New on the Paleo Web Pages for 2009

Figure 1. pCO2 difference between the atmosphere and the ocean for 1995 Enhanced carbon pump inferred from relaxation of nutrient limitation in the glacial ocean
Pichevin et al.
News and Views
Vol 459, No. 7250, pp. 1114-1117, 25 June 2009.

The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments, but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.
Northern Hemisphere interglacial topography and ice cover Interglacial and future sea level
Clark and Huybers
News and Views
Vol. 462, No. 7275, pp. 856-857, 17 December 2009

A merger of data and modelling using a probabilistic approach indicates that sea level was much higher during the last interglacial than it is now, providing telling clues about future ice-sheet responses to warming.
Sofular Cave Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey
Fleitmann et al. Geophysical Research Letters
Vol. 36, L19707, doi:10.1029/2009GL040050

A 50 kyr-long exceptionally well-dated and highly resolved stalagmite oxygen (δ18O) and carbon (δ13C) isotope record from Sofular Cave in northwestern Turkey helps to further improve the dating of Greenland Interstadials (GI) 1, and 3-12. Timing of most GI in the Sofular record is consistent within ±10 to 300 years with the "iconic" Hulu Cave record. Larger divergences (>500 years) between Sofular and Hulu are only observed for GI 4 and 7. The Sofular record differs from the most recent NGRIP chronology by up to several centuries, whereas age offsets do not increase systematically with depth. The Sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern Mediterranean to GI, whereas a phase lag of ~100 years between climate and full ecosystem response is evident. Finally, results of spectral analyses of the Sofular isotope records do not support a 1,470-year pacing of GI.
Satellite image of Antarctica.  NASA/Goddard Space Flight Center, Scientific Visualization Studio Atmospheric carbon dioxide through the Eocene-Oligocene climate transition
Pearson et al. Nature
Vol. 461, pp. 1110-1113, 22 October 2009 doi:10.1038/nature08447

Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (P CO2atm) fell below a critical threshold of 750 p.p.m.v., but the timing and magnitude of P CO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate P CO2atm before, during and after the climate transition.
Satellite image of the Alps, Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC  High-resolution isotope records of early Holocene rapid climate change from two coeval stalagmites of Katerloch Cave, Austria
Boch et al. Quaternary Science Reviews
Vol. 28, pp. 2527-2538, November 2009

Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ18O values around 8.2, 9.1, and 10.0 kyr. The 8.2 kyr climate anomaly lasted about one century, from 8196 to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr. The event is characterized by a rapid onset within 10-20 yr and a more gradual demise. Our record also shows a distinct climate anomaly around 9.1 kyr, which lasted 70-110 yr and showed a maximum amplitude of 1.0‰. Moreover, both stalagmites show evidence of a climate anomaly around 10.0 kyr, which was of comparable magnitude to the two subsequent events. Maximum cooling by ca 3°C can be inferred at 8.2 and 9.1 kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps.
Liang Luar Cave, Flores, Indonesia Increasing Australian-Indonesian monsoon rainfall linked to early Holocene sea-level rise
Griffiths et al. Nature GeoScience
Vol. 2, No. 9, pp. 636-639, September 2009

The Australian-Indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical Indo-Pacific region. It has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation, but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult, owing to the lack of high-resolution records of past monsoon behaviour. Here we present a precisely dated reconstruction of monsoon rainfall over the past 12,000 years, based on oxygen isotope measurements from two stalagmites collected in southeast Indonesia. We show that the summer monsoon precipitation increased during the Younger Dryas cooling event, when Atlantic meridional overturning circulation was relatively weak. Monsoon precipitation intensified even more rapidly from 11,000 to 7,000 years ago, when the Indonesian continental shelf was flooded by global sea-level rise. We suggest that the intensification during the Younger Dryas cooling was caused by enhanced winter monsoon outflow from Asia and a related southward migration of the intertropical convergence zone. However, the early Holocene intensification of monsoon precipitation was driven by sea-level rise, which increased the supply of moisture to the Indonesian archipelago.
Figure 1. Locations of the documentary records and fraction of explained precipitation variance An extended network of documentary data from South America and its potential for quantitative precipitation reconstructions back to the 16th century
Neukom et al. Geophysical Research Letters
Vol. 36, 2009, L12703, doi:10.1029/2009GL038351

In South America (SA) several documentary based climate time series exist, some of them extending back to the 16th century. Most of these records end in the 19th century, and can not be calibrated against instrumental data. Here, we used the newspaper "Los Andes" from Mendoza, Argentina, to extend documentary based indices of Mendoza precipitation and Central Andes snow depth to the late 20th century. A statistical approach to create "pseudo documentary" 20th century data was applied to prolong eight other documentary records. Increased variability of the hydrological cycle in the Central Andes and prevailing periods of wet and dry years in Mendoza suggest that the 20th century is extraordinary in the context of the last 400 years. The final set of extended documentaries explains significant portions of SA precipitation variability in large areas between 20°S and 40°S and can therefore improve the network of annually resolved precipitation proxies.
Fig. 1. Locations of the proxy climate records included in the synthesis Recent warming reverses long-term Arctic cooling
Kaufman et al. Science
Vol. 325, No. 5945, pp. 1236-1239, 4 September 2009.

The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.
World Ocean Atlas 2005 Sea Surface Temperature, Indo-Pacific Warm Pool. NOAA/NODC image 2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool
Oppo et al. Nature
Vol. 460, No. 7259, pp. 1113-1116, 27 August 2009. doi:10.1038/nature08233

Northern Hemisphere surface temperature reconstructions suggest that the late twentieth century was warmer than any other time during the past 500 years and possibly any time during the past 1,300 years. These temperature reconstructions are based largely on terrestrial records from extra-tropical or high-elevation sites; however, global average surface temperature changes closely follow those of the global tropics, which are 75% ocean. In particular, the tropical Indo-Pacific warm pool (IPWP) represents a major heat reservoir that both influences global atmospheric circulation and responds to remote northern high- latitude forcings. Here we present a decadally resolved continuous sea surface temperature (SST) reconstruction from the IPWP that spans the past two millennia and overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends. Our record from the Makassar Strait, Indonesia, exhibits trends that are similar to a recent Northern Hemisphere temperature reconstruction. Reconstructed SST was, however, within error of modern values from about AD 1000 to AD 1250, towards the end of the Medieval Warm Period. SSTs during the Little Ice Age (approximately AD 1550-1850) were variable, and ~0.5° to 1°C colder than modern values during the coldest intervals. A companion reconstruction of δ18O of sea water - a sea surface salinity and hydrology indicator - indicates a tight coupling with the East Asian monsoon system and remote control of IPWP hydrology on centennial-millennial timescales, rather than a dominant influence from local SST variation.
Rock Hyrax A record of rapid Holocene climate change preserved in hyrax middens from southwestern Africa
Chase et al. Geology
Vol. 37, No. 8, pp. 703-706, August 2009. doi: 10.1130/G30053A.1.

The discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central Namib Desert, Africa, is providing unprecedented insight into the region's environmental history. High-resolution stable carbon and nitrogen isotope records spanning 0-11,700 cal (calibrated) yr B.P. indicate phases of relatively humid conditions from 8700-7500, 6900-6700, 5600-4900, and 4200-3500 cal yr B.P., with a period of marked aridity occurring from 3500 until ca. 300 cal yr B.P. Transitions between these phases appear to have occurred very rapidly, often within <200 years. Of particular importance are: (1) the observed relationship between regional aridification and the decline in Northern Hemisphere insolation across the Holocene, and (2) the significance of suborbital scale variations in climate that covary strongly with fluctuations in solar forcing. Together, these elements call for a fundamental reexamination of the role of orbital forcing on tropical African systems, and a reconsideration of what factors drive climate change in the region. The quality and resolution of these data far surpass any other evidence available from the region, and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern Africa.
Glacial Maximum ice sheet extent Deep-Sea Temperature and Ice Volume Changes Across the Pliocene-Pleistocene Climate Transitions
Sosdian and Rosenthal Science
Vol. 325, pp. 306 - 310, 17 July 2009. DOI: 10.1126/science.1169938

Earth has undergone profound changes since the late Pliocene, which led to the development [~2.7 million years ago (Ma)] and intensification (~0.9 Ma) of large-scale Northern Hemisphere ice sheets, recorded as transitions in the benthic foraminiferal oxygen isotope (δ18Ob) record. Here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium/calcium ratios from the North Atlantic, which shows that temperature variations are a substantial portion of the global δ18Ob signal. The record shows two distinct cooling events associated with the late Pliocene (LPT, 2.5 to 3 Ma) and mid-Pleistocene (MPT, 1.2 to 0.85 Ma) climate transitions. Whereas the LPT increase in ice volume is attributed directly to global cooling, the shift to 100,000-year cycles at the MPT is more likely to be a response to an additional change in ice-sheet dynamics.
Massive poirites coral from Ogasawara Islands, Japan Subtropical coral reveals abrupt early-twentieth-century freshening in the western North Pacific Ocean
Felis et al. Geology
Vol. 37, No. 6, pp. 527-530, June 2009. doi:10.1130/G25581A.1

Instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century. Unlike for temperature, continuous salinity observations in the surface ocean are scarce prior to 1970, and the magnitude of salinity changes during the twentieth century is largely unknown. Surface ocean salinity is a major component in climate dynamics, as it influences ocean circulation and water mass formation. Here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical North Pacific Ocean since 1873, based on bimonthly records of δ18O, Sr/Ca, and U/Ca in a coral from the Ogasawara Islands. The reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910. Observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the Kuroshio Current system and the associated subtropical gyre circulation. We note that the abrupt early-twentieth- century freshening in the western subtropical North Pacific precedes abrupt climate change in the northern North Atlantic by a few years. The potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades.
Sea Level Pressure reconstuction, 1750 AD The importance of ship log data: reconstructing North Atlantic, European and Mediterranean sea level pressure fields back to 1750
Küttel et al. Climate Dynamics
Published online 28 April 2009. doi:10.1007/s00382-009-0577-9.

Local to regional climate anomalies are to a large extent determined by the state of the atmospheric circulation. The knowledge of large-scale sea level pressure (SLP) variations in former times is therefore crucial when addressing past climate changes across Europe and the Mediterranean. However, currently available SLP reconstructions lack data from the ocean, particularly in the pre-1850 period. Here we present a new statistically-derived 5° x 5° resolved gridded seasonal SLP dataset covering the eastern North Atlantic, Europe and the Mediterranean area (40°W - 50°E; 20°N - 70°N) back to 1750 using terrestrial instrumental pressure series and marine wind information from ship logbooks. For the period 1750-1850, the new SLP reconstruction provides a more accurate representation of the strength of the winter westerlies as well as the location and variability of the Azores High than currently available multiproxy pressure field reconstructions. These findings strongly support the potential of ship logbooks as an important source to determine past circulation variations especially for the pre-1850 period. This new dataset can be further used for dynamical studies relating large-scale atmospheric circulation to temperature and precipitation variability over the Mediterranean and Eurasia, for the comparison with outputs from GCMs as well as for detection and attribution studies.
Antarctica, NASA/Goddard Space Flight Center Scientific Visualization Studio Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2
Anderson et al. Science
Vol. 323, No. 5920, pp. 1443-1448, 13 March 2009.

Wind-driven upwelling in the ocean around Antarctica helps regulate the exchange of carbon dioxide (CO2) between the deep sea and the atmosphere, as well as the supply of dissolved silicon to the euphotic zone of the Southern Ocean. Diatom productivity south of the Antarctic Polar Front and the subsequent burial of biogenic opal in underlying sediments are limited by this silicon supply. We show that opal burial rates, and thus upwelling, were enhanced during the termination of the last ice age in each sector of the Southern Ocean. In the record with the greatest temporal resolution, we find evidence for two intervals of enhanced upwelling concurrent with the two intervals of rising atmospheric CO2 during deglaciation. These results directly link increased ventilation of deep water to the deglacial rise in atmospheric CO2.
North Atlantic Sea Surface Temperature map Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly
Trouet et al. Science
Vol. 324, No. 5923, pp. 78-80, 3 April 2009.

The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña-like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.
Bear Lake, Utah - Idaho Paleoenvironments of Bear Lake, Utah and Idaho, and Its Catchment
Geological Society of America Special Paper 450

Bear Lake is located 100 km northeast of Salt Lake City and lies along the course of the Bear River, the largest river in the Great Basin. The lake, which is one of the oldest extant lakes in North America, occupies a tectonically active half-graben and contains hundreds of meters of Quaternary sediment. This volume is the culmination of more than a decade of coordinated investigations aimed at a holistic understanding of this long-lived alkaline lake in the semiarid western United States. Its 14 chapters, with 20 contributing authors, contain geological, mineralogical, geochemical, paleontological, and limnological studies extending from the drainage basin to the depocenter. The studies span both modern and paleoenvironments, including a 120-m-long sediment core that captures a continuous record of the last two glacial-interglacial cycles.
IPCC temperature reconstructions plot NOAA Paleoclimatology Reconstructions Network
NOAA Paleoclimatology has released the first product of its Paleoclimate Network (PCN), including 92 high-resolution temperature records over the past 2+ millennia in its archive. These records include global, hemispheric, regional, and local reconstructions, generally with annual time-step resolution. The records come with many categories of metadata. Each record is available as a separate ASCII file with fixed header and data formats, allowing machine reading of the data and time-step information. All the records together are also available in netCDF, ASCII, and Excel formats, including the complete metadata within the files themselves.
Cascade Lake, Ahklun Mountains, Alaska Late Holocene Climatic and Environmental Change Inferred from Arctic Lake Sediments
Journal of Paleolimnology Special Volume
Volume 41, Number 1, January 2009

The 14 papers in this Special Issue of the Journal of Paleolimnology report new records of Holocene climate and environmental change from Arctic lakes, with emphasis on the last 2000 years. The study sites span the high latitudes of North America and extend into northwestern Europe. The studies rely on multiple proxy indicators to reconstruct past climate, including: varve thicknesses, chironomid, diatom, and pollen assemblages, biogenic-silica and organic-matter content, oxygen-isotope ratios in diatoms, and the frequency of lake-ice-rafted aggregates. These proxies primarily document changes in past summer temperatures, the main control on physical and biological processes in lakes at high latitudes. The records will be integrated into a larger network of paleoclimate sites to investigate the spatial and temporal variability of climate change and to compare the paleoclimate inferences with the output of general circulation models.
Great Barrier Reef satellite image, NASA/GSFC/LaRC/JPL, MISR Team Declining Coral Calcification on the Great Barrier Reef
De'ath et al. Science
Vol. 323, No. 5910, pp. 116-119, 2 January 2009. doi: 10.1126/science.1165283

Reef-building corals are under increasing physiological stress from a changing climate and ocean absorption of increasing atmospheric carbon dioxide. We investigated 328 colonies of massive Porites corals from 69 reefs of the Great Barrier Reef (GBR) in Australia. Their skeletal records show that throughout the GBR, calcification has declined by 14.2% since 1990, predominantly because extension (linear growth) has declined by 13.3%. The data suggest that such a severe and sudden decline in calcification is unprecedented in at least the past 400 years. Calcification increases linearly with increasing large-scale sea surface temperature but responds nonlinearly to annual temperature anomalies. The causes of the decline remain unknown; however, this study suggests that increasing temperature stress and a declining saturation state of seawater aragonite may be diminishing the ability of GBR corals to deposit calcium carbonate.

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