Tierney
Jessica E.
Tierney
Jessica E.
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PreprintThe effect of sea level on glacial Indo-Pacific climate( 2013-03-25) DiNezio, Pedro N. ; Tierney, Jessica E.The Indo-Pacific Warm Pool – the Earth’s largest body of warm water and main source of heat and moisture to the global atmosphere – plays a prominent role in tropical and global climate change. The physical mechanisms driving changes in the warm pool over glacial-interglacial timescales are largely unknown. Here we show that during the Last Glacial Maximum (LGM) changes in global sea level influenced tropical climate by exposing the Sunda Shelf and altering the Walker Circulation. Our result is based on a synthesis of marine and terrestrial proxies sensitive to hydroclimate and a multi-model ensemble of climate simulations. The proxy data suggest drying throughout the warm pool, and wetter conditions in the western Indian and Pacific oceans. Only one model out of twelve simulates a similar pattern of hydroclimate change, as measured by the Cohen’s statistic. According to this model, weakened convection over the warm pool in response to exposure of the Sunda Shelf drives the proxy-inferred hydrological changes. Our study demonstrates that on glacial-interglacial timescales, ice sheets exert a first order influence on tropical climate through changes in global sea level.
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ArticleCoordinated hydrological regimes in the Indo-Pacific region during the past two millennia(American Geophysical Union, 2010-03-05) Tierney, Jessica E. ; Oppo, Delia W. ; Rosenthal, Yair ; Russell, James M. ; Linsley, Braddock K.Instrumental data suggest that major shifts in tropical Pacific atmospheric dynamics and hydrology have occurred within the past century, potentially in response to anthropogenic warming. To better understand these trends, we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes (δDwax) in marine sediments from southwest Sulawesi, Indonesia, to compile a detailed reconstruction of central Indo-Pacific Warm Pool (IPWP) hydrologic variability spanning most of the last two millennia. Our paleodata are highly correlated with a monsoon reconstruction from Southeast Asia, indicating that intervals of strong East Asian summer monsoon (EASM) activity are associated with a weaker Indonesian monsoon (IM). Furthermore, the centennial-scale oscillations in our data follow known changes in Northern Hemisphere climate (e.g., the Little Ice Age and Medieval Warm Period) implying a dynamic link between Northern Hemisphere temperatures and IPWP hydrology. The inverse relationship between the EASM and IM suggests that migrations of the Intertropical Convergence Zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the IPWP throughout most of the past two millennia.
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ArticleThe influence of Indian Ocean atmospheric circulation on Warm Pool hydroclimate during the Holocene epoch(American Geophysical Union, 2012-10-04) Tierney, Jessica E. ; Oppo, Delia W. ; LeGrande, Allegra N. ; Huang, Yongsong ; Rosenthal, Yair ; Linsley, Braddock K.Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September–November (SON) season is important for hydroclimate in Borneo. The preëminence of the SON season suggests that a seasonally lagged relationship between the Indian
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PreprintIdentifying coherent spatiotemporal modes in time-uncertain proxy paleoclimate records( 2012-07) Anchukaitis, Kevin J. ; Tierney, Jessica E.High-resolution sedimentary paleoclimate proxy records offer the potential to expand the detection and analysis of decadal- to centennial-scale climate variability during recent millennia, particularly within regions where traditional high-resolution proxies may be short, sparse, or absent. However, time uncertainty in these records potentially limits a straightforward objective identification of broad-scale patterns of climate variability. Here, we describe a procedure for identifying common patterns of spatiotemporal variability from time uncertain sedimentary records. This approach, which we term Monte Carlo Empirical Orthogonal Function (MCEOF) analysis, uses iterative age modeling and eigendecomposition of proxy time series to isolate common regional patterns and estimate uncertainties. As a test case, we apply this procedure to a diverse set of time-uncertain lacustrine proxy records from East Africa. We also perform a pseudoproxy experiment using climate model output to examine the ability of the method to extract shared anomalies given known signals. We discuss the advantages and disadvantages of our approach, including possible extensions of the technique.
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ArticleA TEX86 surface sediment database and extended Bayesian calibration(Nature Publishing Group, 2015-06-23) Tierney, Jessica E. ; Tingley, Martin P.Quantitative estimates of past temperature changes are a cornerstone of paleoclimatology. For a number of marine sediment-based proxies, the accuracy and precision of past temperature reconstructions depends on a spatial calibration of modern surface sediment measurements to overlying water temperatures. Here, we present a database of 1095 surface sediment measurements of TEX86, a temperature proxy based on the relative cyclization of marine archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids. The dataset is archived in a machine-readable format with geospatial information, fractional abundances of lipids (if available), and metadata. We use this new database to update surface and subsurface temperature calibration models for TEX86 and demonstrate the applicability of the TEX86 proxy to past temperature prediction. The TEX86 database confirms that surface sediment GDGT distribution has a strong relationship to temperature, which accounts for over 70% of the variance in the data. Future efforts, made possible by the data presented here, will seek to identify variables with secondary relationships to GDGT distributions, such as archaeal community composition.
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ArticleSouth Pacific hydrologic and cyclone variability during the last 3000 years(John Wiley & Sons, 2016-04-18) Toomey, Michael R. ; Donnelly, Jeffrey P. ; Tierney, Jessica E.Major excursions in the position of the South Pacific Convergence Zone (SPCZ) and/or changes in its intensity are thought to drive tropical cyclone (TC) and precipitation variability across much of the central South Pacific. A lack of conventional sites typically used for multimillennial proxy reconstructions has limited efforts to extend observational rainfall/TC data sets and our ability to fully assess the risks posed to central Pacific islands by future changes in fresh water availability or the frequency of storm landfalls. Here we use the sedimentary record of Apu Bay, offshore the island of Tahaa, French Polynesia, to explore the relationship between SPCZ position/intensity and tropical cyclone overwash, resolved at decadal time scales, since 3200 years B.P. Changes in orbital precession and Pacific sea surface temperatures best explain evidence for a coordinated pattern of rainfall variability at Tahaa and across the Pacific over the late Holocene. Our companion record of tropical cyclone activity from Tahaa suggests major storm activity was higher between 2600-1500 years B.P., when decadal scale SPCZ variability may also have been stronger. A transition to lower storm frequency and a shift or expansion of the SPCZ toward French Polynesia around 1000 years B.P. may have prompted Polynesian migration into the central Pacific.
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PreprintExtremes in East African hydroclimate and links to Indo-Pacific variability on interannual to decadal timescales( 2017-07) Ummenhofer, Caroline C. ; Kulüke, Marco ; Tierney, Jessica E.East African hydroclimate exhibits considerable variability across a range of timescales, with implications for its population that depends on the region’s two rainy seasons. Recent work demonstrated that current state-of-the-art climate models consistently underestimate the long rains in boreal spring over the Horn of Africa while overestimating the short rains in autumn. This inability to represent the seasonal cycle makes it problematic for climate models to project changes in East African precipitation. Here we consider whether this bias also has implications for understanding interannual and decadal variability in the East African long and short rains. Using a consistent framework with an unforced multi-century global coupled climate model simulation, the role of Indo-Pacific variability for East African rainfall is compared across timescales and related to observations. The dominant driver of East African rainfall anomalies critically depends on the timescale under consideration: Interannual variations in East African hydroclimate coincide with significant sea surface temperature (SST) anomalies across the Indo-Pacific, including those associated with the El Niño-Southern Oscillation (ENSO) in the eastern Pacific, and are linked to changes in the Walker circulation, regional winds and vertical velocities over East Africa. Prolonged drought/pluvial periods in contrast exhibit anomalous SST predominantly in the Indian Ocean and Indo-Pacific warm pool (IPWP) region, while eastern Pacific anomalies are insignificant. We assessed dominant frequencies in Indo-Pacific SST and found the eastern equatorial Pacific dominated by higher-frequency variability in the ENSO band, while the tropical Indian Ocean and IPWP exhibit lower-frequency variability beyond 10 years. This is consistent with the different contribution to regional precipitation anomalies for the eastern Pacific versus Indian Ocean and IPWP on interannual and decadal timescales, respectively. In the model, the dominant low-frequency signal seen in the observations in the Indo-Pacific is not well-represented as it instead exhibits overly strong variability on subdecadal timescales. The overly strong ENSO-teleconnection likely contributes to the overestimated role of the short rains in the seasonal cycle in the model compared to observations.
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ArticleTropical sea surface temperatures for the past four centuries reconstructed from coral archives(John Wiley & Sons, 2015-03-18) Tierney, Jessica E. ; Abram, Nerilie J. ; Anchukaitis, Kevin J. ; Evans, Michael N. ; Giry, Cyril ; Kilbourne, K. Halimeda ; Saenger, Casey P. ; Wu, Henry C. ; Zinke, JensMost annually resolved climate reconstructions of the Common Era are based on terrestrial data, making it a challenge to independently assess how recent climate changes have affected the oceans. Here as part of the Past Global Changes Ocean2K project, we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics, based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives. Validation exercises suggest that our reconstructions are interpretable for much of the past 400 years, depending on the availability of paleoclimate data within, and the reconstruction validation statistics for, each target region. Analysis of the trends in the data suggests that the Indian, western Pacific, and western Atlantic Ocean regions were cooling until modern warming began around the 1830s. The early 1800s were an exceptionally cool period in the Indo-Pacific region, likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century. Decadal-scale variability is a quasi-persistent feature of all basins. Twentieth century warming associated with greenhouse gas emissions is apparent in the Indian, West Pacific, and western Atlantic Oceans, but we find no evidence that either natural or anthropogenic forcings have altered El Niño–Southern Oscillation-related variance in tropical sea surface temperatures. Our marine-based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change.
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ArticleLipid biomarker record documents hydroclimatic variability of the Mississippi River Basin during the common era(Wiley, 2020-05-30) Munoz, Samuel E. ; Porter, Trevor J. ; Bakkelund, Aleesha ; Nusbaumer, Jesse ; Dee, Sylvia G. ; Hamilton, Brynnydd ; Giosan, Liviu ; Tierney, Jessica E.Floods and droughts in the Mississippi River basin are perennial hazards that cause severe economic disruption. Here we develop and analyze a new lipid biomarker record from Horseshoe Lake (Illinois, USA) to evaluate the climatic conditions associated with hydroclimatic extremes that occurred in this region over the last 1,800 years. We present geochemical proxy evidence of temperature and moisture variability using branched glycerol dialkyl glycerol tetraethers (brGDGTs) and plant leaf wax hydrogen isotopic composition (δ2Hwax) and use isotope‐enabled coupled model simulations to diagnose the controls on these proxies. Our data show pronounced warming during the Medieval era (CE 1000–1,600) that corresponds to midcontinental megadroughts. Severe floods on the upper Mississippi River basin also occurred during the Medieval era and correspond to periods of enhanced warm‐season moisture. Our findings imply that projected increases in temperature and warm‐season precipitation could enhance both drought and flood hazards in this economically vital region.
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ArticleGDGT and alkenone flux in the northern Gulf of Mexico : implications for the TEX86 and UK'37 paleothermometers(John Wiley & Sons, 2016-12-19) Richey, Julie N. ; Tierney, Jessica E.The TEX86 and UKˈ37 molecular biomarker proxies have been broadly applied in downcore marine sediments to reconstruct past sea surface temperature (SST). Although both TEX86 and UKˈ37 have been interpreted as proxies for mean annual SST throughout the global ocean, regional studies of glycerol dibiphytanyl glycerol tetraethers (GDGTs) and alkenones in sinking particles are required to understand the influence of seasonality, depth distribution, and diagenesis on downcore variability. We measure GDGT and alkenone flux, as well as the TEX86 and UKˈ 37 indices in a 4 year sediment trap time series (2010–2014) in the northern Gulf of Mexico (nGoM), and compare these data with core-top sediments at the same location. GDGT and alkenone fluxes do not show a consistent seasonal cycle; however, the largest flux peaks for both occurs in winter. UKˈ 37 covaries with SST over the 4 year sampling interval, but the UKˈ 37-SST relationship in this data set implies a smaller slope or nonlinearity at high temperatures when compared with existing calibrations. Furthermore, the flux-weightedUKˈ 37 value from sinking particles is significantly lower than that of underlying core-top sediments, suggesting preferential diagenetic loss of the tri-unsaturated alkenone in sediments. TEX86 does not covary with SST, suggesting production in the subsurface upper water column. The flux-weighted mean TEX86 matches that of core-top sediments, confirming that TEX86 in the nGoM reflects local planktonic production rather than allochthonous or in situ sedimentary production. We explore potential sources of uncertainty in both proxies in the nGoM but demonstrate that they show nearly identical trends in twentieth century SST, despite these factors.
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ArticleHydroclimate variability in the equatorial western Indian Ocean for the last 250,000 years(American Geophysical Union, 2023-01-21) Windler, Grace ; Tierney, Jessica E. ; deMenocal, Peter B.Abstract Indian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean-atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19-193 (2.98°N, 51.47°E) that span the last 250 ky. Sub-surface water temperatures (Sub-T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial-interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo-Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin-wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19-193 indicate that both precession and glacial-interglacial cycles exert control over hydroclimate at this tropical location.