Brachert, T. C., Reuter, M., Krüger, S., Lohmann, H., Petuch, E. J., & Klaus, J. S. (2014). A 4.2 million years record of interglacial paleoclimate from sclerochronological data of Florida carbonate platform (Early Pliocene to recent). Global and Planetary Change, 120, 54–64.
Abstract: The climate of the Pliocene and early Pleistocene was in a transient mode from generally warmer climates of the early Neogene to the maximum glaciations of the late Quaternary. Increasingly severe coolings occurred episodically in the high latitudes, whereas the low latitudes remained warm. For the last 5 million years (Ma), rather constant sea surface temperatures have been recorded in the Western Atlantic warm pool; however, direct climate data on temperature and humidity from shallow near-shore settings are lacking so far. In this study we present a synthesis of 26 new and 46 (incl. 24 recent) published sclerochronogical stable isotope records (18O/16O, 13C/12C) with a sub-annual resolution from reef corals (z-corals) and mollusks. The fossils were sampled from shallow-water carbonate deposits of the Florida carbonate platform and belong to 12 interglacial time-slices spanning collectively the period from the Early Pliocene to the recent (4.2 to 0 Ma). Although platform carbonates are believed to undergo rapid diagenetic stabilization due to the dissolution of metastable aragonite shells, we show that there is still a wealth of material to be recovered for large-scale systematic geochemical studies. We rule out significant diagenetic modifications of the stable isotope data because measured 18O/16O ratios from z-corals and mollusks converted into temperature give consistent results. Accordingly, annual mean temperatures have risen during the last 4.2 Ma from ~ 23 °C to 26 °C in open waters, given the modern seawater value of 18O/16O is valid for Neogene. However, the global water value has changed due to long-term increases in ice volume even during interglacials, equivalent with a 2.3 °C temperature rise. A net 5.3 °C temperature increase over the last 4.2 Ma is inconsistent with the deep-sea record, however, and suggestive of an overall increase of humidity effects in measured 18O/16O instead. Particularly cool temperatures have been registered at 1.9 and 2.5 Ma, but combined 18O/16O and 13C/12C data identify these as artifacts from intensified evaporation which fits the overall restricted marine aspect of the fossil fauna in these time-slices. Seasonal temperature contrasts seem to have been high within restricted settings (~ 11 °C) and small in mixed open marine units (7–8 °C). Although this finding fits the modern situation with coastal environments undergoing 14 °C seasonal change and the reef tract 7–9 °C only, circumstantial evidence suggests reconstructions to be biased by sub-annual changes in the local seawater value for 18O/16O. Since 18O/16O seasonality has increased over the last 4.2 Ma, we suggest the humidity of modern Florida to have evolved from dryer precursor climates of past interglacials, whereas temperatures in essence remained the same. This trend possibly represents the expression of the growing relevance of the Bermudas High pressure cell. Glacial climates of Florida cannot be reconstructed using our methodology as the Florida platform was emergent during sea level lowstands.
|
Erb, M. P., Broccoli, A. J., Graham, N. T., Clement, A. C., Wittenberg, A. T., & Vecchi, G. A. (2015). Response of the Equatorial Pacific Seasonal Cycle to Orbital Forcing. J. Climate, 28(23), 9258–9276.
Abstract: The response of the equatorial Pacific Ocean's seasonal cycle to orbital forcing is explored using idealized simulations with a coupled atmosphere-ocean GCM in which eccentricity, obliquity, and the longitude of perihelion are altered while other boundary conditions are maintained at preindustrial levels. The importance of ocean dynamics in the climate response is investigated using additional simulations with a slab ocean version of the model. Precession is found to substantially influence the equatorial Pacific seasonal cycle through both thermodynamic and dynamic mechanisms, while changes in obliquity have only a small effect. In the precession experiments, western equatorial Pacific SSTs respond in a direct thermodynamic manner to changes in insolation, while the eastern equatorial Pacific is first affected by the propagation of thermocline temperature anomalies from the west. These thermocline signals result from zonal wind anomalies associated with changes in the strength of subtropical anticyclones and shifts in the regions of convection in the western equatorial Pacific. The redistribution of heat from these thermocline signals, aided by the direct thermodynamic effect of insolation anomalies, results in large changes to the strength and timing of the eastern equatorial Pacific seasonal cycle. A comparison of 10 CMIP5 mid-Holocene experiments, in which the primary forcing is due to precession, shows that this response is relatively robust across models. Because equatorial Pacific SST anomalies have local climate impacts as well as nonlocal impacts through teleconnections, these results may be important to understanding paleoclimate variations both inside and outside of the tropical Pacific.
|
Hanna, A. J. M., Shanahan, T. M., Allison, M. A., Bianchi, T. S., & Schreiner, K. M. (2018). A multi-proxy investigation of late-Holocene temperature change and climate-driven fluctuations in sediment sourcing: Simpson Lagoon, Alaska. The Holocene, 28(6), 984–997.
Abstract: The significant and ongoing environmental changes in Arctic regions demonstrate the need for quantitative, high-resolution records of pre-industrial climate change in this climatically sensitive region; such records are fundamental for understanding recent anthropogenic changes in the context of natural variability. Sediment contained within Arctic coastal environments proximal to large fluvial systems has the ability to record paleoclimate variability on subdecadal to decadal scale resolution, on par with many other terrestrial climate archives (i.e. lake sediments, ice cores). Here, we utilize one such sediment archive from Simpson Lagoon, Alaska, located adjacent to the Colville River Delta to reconstruct temperature variability and fluctuations in sediment sourcing over the past 1700 years. Quantitative reconstructions of summer air temperature are obtained using the branched glycerol dialkyl glycerol tetraether (brGDGT)-derived methylation index of branched tetraethers (MBT')/cyclization ratio of branched tetraether (CBT) paleothermometer and reveal temperature departures correlative with noted climate events (i.e. 'Little Ice Age', 'Medieval Climate Anomaly'). In addition, temporal variability in sediment sourcing to the lagoon, determined using a multi-proxy approach (i.e. granulometry, elemental analysis, clay mineralogy), broadly corresponds with temperature fluctuations, indicating relative increases in fluvial sediment discharge during colder intervals and decreased river discharge/increased coastal erosion during warmer periods. The Simpson Lagoon record presented in this study is the first temperature reconstruction, to our knowledge, developed from coastal marine sediments in the Alaskan Beaufort Sea.
|
Hine, A. C., Martin, E. E., Jaeger, J. M., & Brenner, M. (2017). Paleoclimate of Florida. In E. P. Chassignet, J. W. Jones, V. Misra, & J. Obeysekera (Eds.), Florida's climate: Changes, variations, & impacts (pp. 457–484). Gainesville, FL: Florida Climate Institute.
Abstract: We present our understanding of Florida’s paleoclimate for the past ~50 million years (Myr). The paleoclimate of the Florida Platform is closely linked to global paleoclimate. Global climate change over the past 50 Myr is a record of declining atmospheric carbon dioxide, decreasing temperature, and progressive addition of ice sheets. The overall global climate narrative is one of transition from a greenhouse Earth (warm temperatures with higher sea levels) to an icehouse Earth (colder temperatures with lower sea levels). The early 21st century has been a period of extreme climate conditions in Florida, in that we have already seen very low lake levels, including complete drying of some water bodies for the first time in recorded history. Such complete drying was never reported previously and suggests that we have entered a new climate regime in this millennium.
|
|
Liu, J., Wang, Y., Wang, Y., Guan, Y., Dong, J., & Li, T. (2018). A multi-proxy record of environmental changes during the Holocene from the Haolaihure Paleolake sediments, Inner Mongolia. Quaternary International, 479, 148–159.
|
|
Mays, J. L., Brenner, M., Curtis, J. H., Curtis, K. V., Hodell, D. A., Correa-Metrio, A., et al. (2017). Stable carbon isotopes ([delta]13C) of total organic carbon and long-chain n-alkanes as proxies for climate and environmental change in a sediment core from Lake Peten-Itza, Guatemala. J Paleolimnol, 57(4), 307–319.
|
|
Pollock, A., van Beynen, P., DeLong, K., Polyak, V., Asmerom, Y., & Reeder, P. (2016). A mid-Holocene paleoprecipitation record from Belize. Palaeogeography, Palaeoclimatology, Palaeoecology, 463, 103–111.
|
Rosenmeier, M. F., Brenner, M., Hodell, D. A., Martin, J. B., Curtis, J. H., & Binford, M. W. (2016). A model of the 4000-year paleohydrology ([delta]18O) record from Lake Salpeten, Guatemala. Global and Planetary Change, 138, 43–55.
Abstract: A simple mass-balance model provides insights into the influence of catchment vegetation changes and climate variability on the hydrologic and stable oxygen isotope (δ18O) evolution of Lake Salpetén, in the Maya Lowlands of northern Guatemala. Model simulations for the last 4000 years incorporate pollen-inferred changes in vegetation cover and account for 75% of the variance observed in the biogenic carbonate δ18O record from a long lake sediment core. Vegetation-driven hydrologic changes, however, failed to capture the full range of late Holocene sediment core δ18O variability. The model requires incorporation of additional shifts in catchment vegetation cover, inclusion of regional precipitation changes, or likely both, to explain the fluctuations observed in the lake core oxygen isotope record. Climatic interpretation of the model results suggests that there was relatively greater moisture availability between about 2400 and 1800 years ago, but increased δ18O values centered at ~ 3300, 2900, 500, and 200 calendar years before present (cal yr BP) indicate abrupt precipitation decreases. There is evidence for protracted aridity between 1500 and 800 cal yr BP.
|
|
Tynan, S., Opdyke, B., Dutton, A., & Walczak, M. (2017). Late Holocene inter-annual temperature variability reconstructed from the [delta][super:18]O of archaeological_Ostrea angasi_shells. Australian Journal of Earth Sciences, 64(6), 779–791.
|
|
van Beynen, P., Polk, J. S., Asmerom, Y., & Polyak, V. (2017). Late Pleistocene and mid-Holocene climate change derived from a Florida speleothem. Quaternary International, 449, 75–82.
|
