Dripwater and Calcite Geochemistry Variations in a Monitored Bahamas Cave

Paleoceanog and Paleoclimatol

Vieten

Winter

et al. 2020

The sensitivity of tropical Atlantic precipitation patterns to the mean position of the Intertropical Convergence Zone (ITCZ) at different time scales is well-known. However, recent research suggests a more complex behavior of the northern hemispheric tropical rain belt related to the ITCZ in the western tropical Atlantic. Here we present a precisely dated speleothem multi-proxy record from a well-monitored cave in Puerto Rico, covering the period between 46.2 and 15.3 ka. The stable isotope and trace element records document a pronounced response of regional rainfall to abrupt climatic excursions in the North Atlantic across the Last Glacial such as Heinrich stadials and Dansgaard/Oeschger events. The annual to multidecadal resolution of the proxy time series allows substructural investigations of the recorded events. Spectral analysis suggests that multidecadal to centennial variability persisted in the regional hydroclimate mainly during interstadial conditions but also during the Last Glacial Maximum. In particular, we observe a strong agreement between the speleothem proxy data and the strength of the Atlantic meridional overturning circulation, supporting a persistent link of oceanic forcing to regional precipitation. Comparison to other paleo-precipitation records enables the reconstruction of past changes in position, strength, and extent of the ITCZ in the western tropical Atlantic in response to millennial-and orbital-scale global climate change. Plain Language Summary It is important to understand the climatic circumstances of how rainfall in the western tropical Atlantic varies under a changing climate to better manage the water supply for millions of people. However, it is not well understood how rainfall varied in the past, especially during the Last Glacial period, a time of strong climate variability and abrupt climate changes. Here, we use a stalagmite from Puerto Rico to create a new record of past changes in rainfall in this region. For this purpose, we analyzed proxy data that reveal a series of wet and dry periods during the Last Glacial corresponding to rapid global climate shifts. Our rainfall-sensitive stalagmite record captured changes of the tropical rain belt on various timescales and shows that this variability in rainfall is closely connected to changes in the strength of the ocean circulation. This suggests that the link between the ocean and the atmosphere is more robust than previously assumed. The comparison of our record with other rainfall-sensitive records from Central America and the northern Caribbean allows for a detailed reconstruction of the spatial and temporal changes of the western tropical Atlantic rain belt.

Section: Discussionsupporting

confidence: 82%

Persistent Link Between Caribbean Precipitation and Atlantic Ocean Circulation During the Last Glacial Revealed by a Speleothem Record From Puerto Rico

Paleoceanog and Paleoclimatol

Vieten

Winter

et al. 2020

“…The overall positive correlation of δ 18 O and δ 13 C values with Mg/Ca suggests a strong hydrological control of these proxies, as found in other studies (Arienzo et al, 2019;Cruz et al, 2007;Sinclair et al, 2012;Wassenburg et al, 2019). The weaker correlation of Sr/Ca and Ba/Ca with Mg/Ca indicates that additional processes modulate the incorporation of Sr and Ba in the speleothem, reducing the suitability of these elements as hydrological proxies.…”

Section: Interpretation Of the Climate Proxiessupporting

confidence: 74%

Persistent link between Caribbean precipitation and Atlantic Ocean circulation during the Last Glacial revealed by a speleothem record from Puerto Rico

Vieten

Winter

et al. 2020

Preprint

The sensitivity of tropical Atlantic precipitation patterns to the mean position of the Intertropical Convergence Zone (ITCZ) at different time scales is well-known. However, recent research suggests a more complex behavior of the northern hemispheric tropical rain belt related to the ITCZ in the western tropical Atlantic. Here we present a precisely dated speleothem multi-proxy record from a well-monitored cave in Puerto Rico, covering the period between 46.2 and 15.3 ka. The stable isotope and trace element records document a pronounced response of regional rainfall to abrupt climatic excursions in the North Atlantic across the Last Glacial such as Heinrich stadials and Dansgaard/Oeschger events. The annual to multidecadal resolution of the proxy time series allows substructural investigations of the recorded events. Spectral analysis suggests that multidecadal to centennial variability persisted in the regional hydroclimate mainly during interstadial conditions but also during the Last Glacial Maximum. In particular, we observe a strong agreement between the speleothem proxy data and the strength of the Atlantic meridional overturning circulation, supporting a persistent link of oceanic forcing to regional precipitation. Comparison to other paleo-precipitation records enables the reconstruction of past changes in position, strength, and extent of the ITCZ in the western tropical Atlantic in response to millennial-and orbital-scale global climate change.Plain Language Summary It is important to understand the climatic circumstances of how rainfall in the western tropical Atlantic varies under a changing climate to better manage the water supply for millions of people. However, it is not well understood how rainfall varied in the past, especially during the Last Glacial period, a time of strong climate variability and abrupt climate changes. Here, we use a stalagmite from Puerto Rico to create a new record of past changes in rainfall in this region. For this purpose, we analyzed proxy data that reveal a series of wet and dry periods during the Last Glacial corresponding to rapid global climate shifts. Our rainfall-sensitive stalagmite record captured changes of the tropical rain belt on various timescales and shows that this variability in rainfall is closely connected to changes in the strength of the ocean circulation. This suggests that the link between the ocean and the atmosphere is more robust than previously assumed. The comparison of our record with other rainfall-sensitive records from Central America and the northern Caribbean allows for a detailed reconstruction of the spatial and temporal changes of the western tropical Atlantic rain belt.

“…We interpret the offset in cluster (1) to reflect a generally weaker convective activity during the last glacial period compared to modern conditions and associated reduced summer rainfall (e.g., Arienzo et al, 2019;Winter et al, 2020;Lases-Hernandez et al, 2019;2020;Bird et al, 2020). Today, Puerto Rico rainfall is isotopically enriched when it is formed by occasional northerly cold fronts as well as orographic processes of trade winds (Scholl and Murphy, 2014).…”

Section: Applicability Of the Oxygen Isotope Equilibrium Thermometermentioning

confidence: 95%

“…In the tropics, the isotopic composition of precipitation, δ 18 Op, has been attributed to changes in precipitation amount and convective activity (Dansgaard, 1964;Lachniet and Patterson, 2009;Vieten et al, 2018a). Consequently, tropical speleothem δ 18 O values are usually interpreted in terms of this isotopic 'amount effect' (Medina-Elizalde et al, 2010;Arienzo et al, 2019;Lases-Hernandez et al, 2019). However, in the soil and karst above the cave as well as at the surface of a stalagmite, various (disequilibrium) isotope fractionation effects can obscure the interpretation of stable isotopes in speleothem calcite (Weber et al, 2021;Hansen et al, 2019;Carlson et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Last glacial millennial-scale hydro-climate and temperature changes in Puerto Rico constrained by speleothem fluid inclusion δ<sup>18</sup>O and δ<sup>2</sup>H values

Weißbach

Kluge

et al. 2021

Preprint

Abstract. We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that covers the interval between 46.2 to 15.3 ka before present on millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The dataset can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where the first cluster comprises samples from cold and dry periods, such as Heinrich and Greenland stadials, as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials, but also for some from Heinrich Stadial 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation is found negligible. Consequently, variations of last glacial hydro-climate and temperature in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of c. 3 °C during the LGM compared to modern cave temperature. During Heinrich Stadials 2 and 3, reconstructed cave temperatures yield an additional cooling of 2.9 ± 2.6 °C and 4.4 ± 0.6 °C, respectively. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable or only slightly weaker than today.