PP13C-1414
Coherent vertical changes in North Pacific climate dynamics during the last millennium
Understanding the forcing and spatial response of Late Holocene North Pacific climate remains a challenge, particularly with respect to changes that may have occurred in the vertical structure of the atmosphere. Ice core records recovered from different elevations in the St. Elias Mountains (Eclipse Icefield, 3000 masl; PR Col, 5200 masl) reveal similar changes in atmospheric circulation and hydrology over the past 1000 years. Sodium concentrations at both sites calibrated to the strength of the wintertime Aleutian Low increase after ~1250 AD, suggesting on average a deeper low pressure system in the North Pacific during the Late Holocene. At the same time, stable isotope data from the Eclipse ice core display a classic Little Ice Age (LIA)/Medieval Climate Anomaly (MCA) pattern; that is, lower isotope ratios during the LIA, and higher isotope ratios during the MCA. Regardless of the scaling used on the Eclipse isotope data (e.g., temperature, hydrology, or some combination), a distinct drop in isotope ratio occurs just prior to 1200AD, which in general corresponds to the observed changes in sodium records as well as many Pacific paleohydrology records. The coherence of this 13th century change in both the horizontal and vertical sense appears to strengthen arguments related to the El Nino Southern Oscillation, namely that changes in volcanic and solar forcing caused a shift from predominately La Nina conditions during the MCA to predominately El Nino conditions during the LIA.
PP13C-1415
Correlating tidewater glacial meltwater discharge with El Niño-Southern Oscillation in Southern Alaska
Over the past two decades coincident with Arctic climate warming, Alaskan glaciers have experienced significant volume loss with the resulting discharge substantially contributing to rising sea level. This thinning has occurred during a period of pronounced variability in regional climatology and oceanography. However, the meteorological parameters forcing melting have not been well established, as there are few annual records of meltwater discharge directly from large cliff-calving glaciers. To test how meltwater production varies in response to climate forcing, a multi-decadal proxy record of meltwater discharge was established for tidewater glaciers in Disenchantment Bay and in Muir Inlet, Glacier Bay National Park, southern coastal Alaska. 33 piston cores and 8 multicores were collected from 24 stations to measure annual sediment deposition rates over the last several decades. Sedimentary facies, physical properties, and short-lived radioisotopes were used to delineate summertime sediment deposition rates on fortnightly to annual time scales, as tidal and seasonal forcing create distinctly laminated (cyclopels) and annually varved deposits. Magnetic susceptibility, sortable silt, and sediment floc characteristics were used as proxies of meltwater plume competence. Complete varves were identified from cores collected in Disenchantment Bay for up to 22 years (1981-2003) and the period of highest and most variable summer layer thickness at Hubbard Glacier coincides with El Ni ñ o-dominated conditions in the North Pacific from 1990-1995 and a warm phase of the Pacific Decadal Oscillation (PDO). The velocity and competence of the meltwater plume increased in the period 1987-1992, likely associated with the numerous ENSO events that resulted in higher winter precipitation. Hubbard Glacier summer sediment thickness data follow a similar temporal trend as the Alsek River discharge hydrograph, the only currently glacierized basin gaged by the USGS in the region, suggesting that the two drainage basins respond similarly to regional climate forcing. Cross-correlation time-series of Alsek River discharge with temperature and precipitation data from the weather station at Yakutat, AK show that summers with higher mean temperatures correlate with increased discharge and to a lesser extent with the amount of precipitation accumulated during the preceding winter. Two 17-m-long jumbo cores from Muir Inlet contain up to 75 years of complete melt-season deposits and associated spring-neap packages. Multi-taper method and singular spectrum analysis spectral estimation techniques were used to calculate statistically significant periodicity in both the melt season deposit thicknesses and spring-neap package thicknesses for each core. Periodicity in melt season deposit thickness shows that both cores contain significant ENSO signals and that one core (EW0408 60JC) contains significant PDO signals. This research has shown that high-resolution records of fjord sedimentation from tidewater glaciers may be a reliable proxy for past magnitude, duration, and temporal distribution of annual meltwater discharge into Alaskan glacial fjords, thus adding to the climate change record in a sensitive area.
PP13C-1416
A Transition in Atmospheric Moisture Transport as Observed in Stable Isotope Data From Mount Wrangell
Measurements made at the summit of Mount Wrangell in the Saint Elias Mountains during a storm in early August 1980 show a change in δ18O that approaches that normally observed to occur between winter and summer in the same region. We explore the synoptic-scale conditions associated with this storm with a view to understanding the processes responsible for this large change in δ18O. Using a variety of diagnostic techniques including satellite imagery, reanalysis data and back-trajectories, we show that during this event there was a dramatic transition in the atmospheric moisture transport to Mount Wrangell from a sub-tropical source region over the central Pacific to an extra-tropical source region over Siberia. This transition was mediated by the interaction of two synoptic-scale weather systems, the semi-permanent high situated over the northeastern Pacific Ocean and a transient extra-tropical cyclone that entered the Alaska region from the west. The implications that such events have on the reconstruction of climate signals contained in ice cores from the Saint Elias region will be discussed.
PP13C-1417
Rapid Climatic and Oceanographic Changes in the Okhotsk Sea during the Holocene
We report on records of centennial- to millennial-scale climatic changes in the Okhotsk Sea and the adjacent continental Amur river watershed, thereby confirming the significant potential of this realm for paleoclimatic reconstructions. High biogenic productivity, delivery of Ice-Rafted Debris (IRD), highly variable hydrographic conditions, and terrigenous sediment supply by the Amurs drainage system closely interact in this region and form the depositional environment. According to our stratigraphic framework, average sedimentation rates in the hemipelagic sediment cores vary between 30 and 160 cm/kyr. Thus, our study provides insight into rapid climatic changes on millenial and shorter timescales for the last deglaciation and the Holocene. Biogenic opal and chlorines serve as biogenic productivity proxies, elemental compositions derived from XRF-scanning as indicators for riverine sediment supply and sea- ice action. Whereas these datasets provide high-resolution records, stable isotope data of benthic and planktic foraminifera as well as countings of terrestrial pollen and IRD data supplement our results on lower temporal scales. The last deglaciation is characterized by repeated pronounced maxima in IRD and according elemental concentrations, pointing to a high supply of terrigenous siliciclastics. During the Holocene, high-frequency oscillations in Amur river discharge can be correlated to the oxygen isotope record of the Greenland NGRIP ice core. We observe significant cyclicities within the millennial and centennial range with a mid-Holocene shift in the significant frequencies. As these periodicities are partly known from other low-latitudinal, monsoonal reference records, these findings may support the notion of a transmission of low latitude climate forcing to the higher latitudes, possibly via freshwater discharge and latent heat transport by the Amur. From ca. 6.5 kyr BP onwards, we recognize a Holocene climatic optimum in various proxy records, whereas starting at about 4 kyr BP slightly deteriorating colder climatic conditions prevail. Planktic and benthic foraminiferal stable isotope data from the Sakhalin margin suggest high hydrographic variability in discharged freshwater. This in turn influences the stratification of regional surface water masses and the average thermocline depth, as well as the formation of intermediate waters that precondition the ventilation and hydrographic properties of the subarctic North Pacific.
PP13C-1418
Linkage between human activity and environments during the mid-Holocene Hypsithermal climatic interval - Changes in human activity at the Sannai-Maruyama ruins in Japan -
The Sannai-Maruyama site is one of the famous and best-archaeologically researched sites for the ruins in Japan during mid-Holocene because of the greatest, well-developed and long-term existing community during the mid-Holocene (mid-Jomon era). According to archeological researches, the Jomon people had inhabited at the Sannai-Maruyama ruins from 5.9-4.2 +/- 0.1 cal. kyr. B.P.. However, little is know about the continuous record on terrestrial and marine environments around the site. Core KT05-7 PC-02, located only 20 km from the ruin, was recovered in Mutsu Bay in order to reconstruct high-resolutonal time-series records, including quantitative sea surface temperatures (SSTs). The C37 alkenone-SSTs showed definite fluctuation with four high SST periods (8.4-7.9, 7.0-5.9, 5.1-4.1 and 2.3-1.4 cal. kyr B.P.) and with low SST periods (-8.4, 7.9-7.0, 5.9-5.1 and 4.1- 2.3 cal. kyr B.P.), which have periodically fluctuated in 1.0-2.0 kyr intervals with about 1.5-2.0 degree amplitude. Based upon contents of TOC (total organic carbon) and C37 alkenone with TOC/TN (TOC/total nitrogen) ratios indicate that marine biogenic production was low before 7.0 cal. kyr B.P. and definitely elevated between 5.9 and 4.0 cal. kyr B.P. due to the stronger vertical mixing. During the community-prospering periods (between 5.9 and 4.2 +/- 0.1 cal. kyr B.P.), the climate had been improved. High relative abundance of both Castanea and Quercus subgen. Cyclobalanopsis pollens supports the interpretation that the local climate was optimum for human community, which would increase the population. Some discrepancy between warm terrestrial climate and low C37 alkenone-SST between 5.9-5.1 cal. kyr B.P. might be attributed to water column structure different from the modern condition in the Tsugaru Strait. These lines of evidence suggest that high production of marine products such as fishes and shells under terrestrial warm climate at 5.9 cal. kyr B.P. resulted in the establishment of the human community at the Sannai-maruyama site and that sudden marine and terrestrial cooling, evidence by C37 alkenone-SST (by 2 degree) and pollen floras, was responsible for reduced terrestrial food supply, which could have caused the people to give up the Sannai-Maruyama ruin at 4.1 +/- 0.1 cal. kyr B.P.. This timing is very consistent with the decline timing (around 4.0-4.3 within error) of several civilization such as the north Mesopotamian and the Yangtze river civilization. A temperature rise by ~2 degree in the future global warming in this century may be enough for giving a great impact on certain areas of the human community, especially agriculture division, even at contemporary society.
PP13C-1419
The 1,500-year climate oscillation in the mid-latitude North Pacific during the Holocene
Suborbital climate variability during the last glacial period was characterized by a periodicity of 1,470 years, but the expression and spatial distribution of the ~1,500-year oscillation during interglacials are not clear. Here we generated a multi-decade-resolution record of alkenone sea-surface temperatures (summer SST) off central Japan in the northwestern Pacific during the Holocene. The SST record showed centennial and millennial variability with an amplitude of ~1°C through the entire Holocene. Spectral analysis shows that SST variation was expressed in 1560-, 880- and 620-year periods, and the ~1,500 year periodicity was the most pronounced. The SST minima correlate with reduced North Atlantic Deep Water formation events (Bond events) and with SST maxima at the California margin. These findings indicate that the mean latitude of the Northern Westerly and the intensity of the North Pacific High varied through a 1,500-year cycle, and that a climatic link existed between the mid-latitude North Pacific and the high-latitude North Atlantic. The regular pacing at 1,500- year intervals through both the Holocene and the last glacial suggests that the oscillation was a response to external forcing rather than an internal oscillation in the climate system.
PP13C-1420
Paleoenvironmental records since 1300 years AD from the calcite stalagmite in the Yongcheon Cave, Jeju Island, Korea
Yongcheon Cave is located on Jeju Island, the southernmost part of Korea. It is a typical lava tube cave that formed between 0.2~0.4 Ma ago, and includes numerous carbonate speleothems. A 11cm-long stalagmite (YC-1) was collected from its growth position in 2005. The 210Pb dating results show that the top 0.9cm of YC-1 is less than 100 years old with the constant growth rate of 0.033mm/yr. 230Th/234U and 14C dating results show that the stalagmite is about 1,600 years old. Textural and stable isotopic analyses were carried out to infer the paleoclimatic variation during its growth. We have analyzed oxygen and carbon isotopes for 200 samples from the 2.5cm-long, uppermost part with a sampling interval of 0.125mm and for 100 samples from the lower 2.5cm-long part with a sampling interval of 0.250mm. δ18O and δ13C values range from -8.1‰ to -5.8‰ and from -8.1‰ to -1.5‰ (PDB), respectively. Both isotope values show the decreasing trends past 60 years due to global warming (depletion of δ18O= 1.2‰ and δ13C=4‰). Carbon isotopic compositions are more enriched in SGL (zone of Spaced Growth Laminae; δ13C=ca -2.5‰, PDB) than DGL (Zone of Dense Growth Laminae; δ13C=ca -7.5‰). This indicates that the overlying carbonates played relatively more significant role to supply carbon for SGL than DGL. Also more depleted carbon isotopic values in DGL should reflect more influence by organic carbon from overlying soil layers. Carbon isotopic variation also clearly shows the period of the Little Ice Age and coincides with the instrumental records of Northern Hemisphere temperature variation during the last 700 years. This preliminary result implies that the carbon isotopic signals have been affected by groundwater residence time which was related to the intensity of regional precipitation and buffering with overlying carbonates. Further analysis of this stalagmite may promise a great potential for the reconstruction of climate and environmental changes during the last 1,600 years.
PP13C-1421
Speleothem-based Holocene Climate History in Southwestern Oregon
We present a high-resolution reconstruction of Holocene climate using stable isotopes in speleothems from Oregon Caves National Monument (OCNM) in southwestern Oregon, USA (42°N, 123°W). OCNM is strongly influenced by air masses originating in the Pacific Ocean and is strategically situated in an area where storm tracks are entering North America. The age control of the speleothem record is given by 9 U-series dates with an average analytical error of 123 years. Preliminary δ\18O measurements of meteoric waters collected above the cave site indicate a temperature-dependent fractionation of 1.3‰°C-1, which is higher than the fractionation between water and calcite (-0.2‰°C-1), suggesting that the δ\18O of OCNM speleothems is strongly influenced by temperature. Because of precipitation seasonality in southwestern Oregon (wet winters and dry summers) and the rapid transit time of meteoric water through the karst aquifer, our speleothem record reflects mostly changes in cool season climate. The speleothem-based temperature reconstruction indicates that for the past 9000 years the climate of southwestern Oregon was characterized by a general warming trend, consistent with an increase in winter insolation at 45°N. Superimposed on this trend there is higher frequency variability at centennial to multi-decadal timescales. Prolonged cool periods are centered around 7.2 ka, 6.2 ka 5.3, 3.5 ka and 1.9 ka, while warm intervals are centered around 6.1 ka, 5.1 ka 4 ka and 1.1 ka. We note that the period corresponding to the Medieval Warm Period (~800 to 1300 AD) has the highest δ\18O values in our record and is characterized by two warm periods interrupted by a cooler period. The Little Ice Age period (~1350 to 1850 AD) is not very clearly expressed in our record as a cold interval, this period being characterized by significant decadal and centennial variability with both warmer and cooler intervals.
PP13C-1422
Response of California Current forcing to mid-Holocene insolation and sea surface temperatures
We find that mid-Holocene insolation causes systematic changes in wind forcing of the California Current System, suppressing wind stress in the spring and enhancing wind stress in the summer and autumn. Both large- and regional-scale processes play an important role in the insolation-enhancement of wind stress, with elevated summer insolation magnifying both large-scale sea level pressure gradients and regional-scale land- sea thermal contrast. We find that prescribed changes in large-scale sea surface temperatures (SSTs) amplify the response of nearshore wind stress to mid-Holocene insolation, with SST-magnification of changes in large- scale sea level pressure gradients overcoming SST-muting of changes in regional-scale land-sea thermal contrast. The climate model simulations are supported by proxy-inferred cooler-than-present sea surface temperatures in the northern California Current System, as well as by high nitrogen isotope values in the southern California Current System. Our results highlight the importance of multi-scale dynamical interactions in regulating the response of regional environments to global-scale changes in radiative forcing.
PP13C-1423
A high-resolution, Holocene record of climate variability from the Eastern North Pacific
Determining climate variations over the Holocene requires high-resolution records with well-developed age models. One such record is provided by marine sediments from Effingham Inlet, an anoxic fjord on the west coast of Vancouver Island, Canada. The present-day regional climate is dominated by the Aleutian Low during winter months and an associated downwelling-favorable wind regime, and by the North Pacific High and upwelling- favourable winds during summer months. Forty-six 14C AMS dates, determined from terrestrial plant material, comprise the new age model for the Effingham core. Downcore sampling at both 5 cm (20 yr) and 1.5 cm (6 yr) resolution indicates high frequency variability at this site over last 14,000 years. Spectral analysis of % opal, a proxy of productivity in the basin, has identified two strong cycles of environmental change identified with the bi- decadal and penta-decadal changes in the Pacific Decadal Oscillation (PDO) and the strength of the Aleutian Low as previously described by Minobe et al. (1999). Comparisons of the Effingham Inlet data with delta180 records from Jellybean Lake (SW Yukon) and the Port McNeil Speleothem (northeastern Vancouver Island) suggest broad regional coherence between productivity in Effingham Inlet, changes in the Aleutian Low strength, and air temperature. In addition to high frequency variations, six periods of diminished basin productivity are identified, each lasting approximately 500 years.
PP13C-1424
Abrupt Changes in the Post-glacial and Paleo-environmental History of the West Coast of Canada
Our continuing studies of annually laminated marine sediments in anoxic fjords along the west coast of Canada chronicle changes in the Holocene environment as glaciers retreated from this area about 12 ky BP, and are shedding new light on the nature and timing of abrupt "regime" shifts in coastal ocean dynamics and climate. We are refining our knowledge of the interplay between climate, ecosystems, and ocean dynamics in the northeast Pacific Ocean, with new perspectives from a diverse suite of proxy indicators including archaeological evidence from pre-historical aboriginal settlement sites, modern oceanographic and meteorological data, and landscape changes associated with recent record-breaking storms and sea surges. The Late Pleistocene and Holocene record on this coast also marks dramatic changes in sea level, with implications for the possibility of early human migration routes and glacial refugia. Excellent chronological control on Holocene paleoclimatic and paleoceanographic conditions along the British Columbia coast is now possible by complementary, yet independent, dating methods of ocean sediments in a giant 40 m piston core which is now being used as a chronological tie point for other proxy records from this area.
PP13C-1425
Palynological Evidence for Late Quaternary Climate and Marine Productivity Changes Along the California Margin
The sedimentary records of dinoflagellate cysts and foraminiferal organic linings from Ocean Drilling Program Holes 1017E (California Margin) and 893A (Santa Barbara Basin) indicate strong response of marine productivity to major shifts in climate and ocean circulation along the California Margin over the past 42 kyr. Throughout the sequences, dinoflagellate cyst assemblages are dominated by upwelling-related taxa, indicating the continued influence of coastal upwelling on the Margin during the Late Quaternary. The cyst records suggest that marine productivity was enhanced during the Holocene and Bolling, and to a lesser extent, during the Last Glacial Maxima and Dansgaard-Oeschger events, while an apparent reduction in productivity can be seen during the Younger Dryas. Comparison between these two sedimentary records allows us to identify local and regional paleoenvironmental signals. For example, the Allerod manifests itself in the enhancement of local marine productivity in the Santa Barbara Basin compared to a regional signal from the California Margin. Our results also indicate noticeable climate variability during the Holocene in this region. Application of the modern dinoflagellate-cyst assemblage-database from the Northeastern Pacific quantitatively indicates that Holocene August sea-surface temperature, salinity and annual marine productivity varied over dynamic ranges of 13-15°C, 24-33 psu, 200-330 gC m-2 yr-1, respectively.