Warm Middle Jurassic–Early Cretaceous high-latitude sea-surface temperatures from the Southern Ocean (original) (raw)
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The duration and magnitude of Cretaceous cool events: Evidence from the northern high latitudes
GSA Bulletin, 2019
The Early Cretaceous (145–100 Ma) was characterized by long-term greenhouse climates, with a reduced equatorial to polar temperature gradient, although an increasingly large body of evidence suggests that this period was punctuated by episodic global “cold snaps.” Understanding climate dynamics during this high-atmospheric CO2 period of Earth’s history may have significant impact on how we understand climatic feedbacks and predict future global climate changes under an anthropogenically-driven high-pCO2 atmosphere. This study utilizes facies analysis to constrain the paleobathymetry of Lower Cretaceous glendonites—a pseudomorph after ikaite, a mineral that forms naturally at 7 °C or lower—from two paleo-high-latitude (60–70°N) sites in Svalbard, Arctic Norway, to infer global climatic changes during the Early Cretaceous. The original ikaite formed in the offshore transition zone of a shallow marine shelf at water depths of <100 m, suggesting mean annual water temperatures of ≤7 °...
Clumped isotope evidence for Early Jurassic extreme polar warmth and high climate sensitivity
2021
Periods of high atmospheric CO 2 levels during the Cretaceous-early Paleogene (∼ 140 to 34 Myr ago) were marked by very high polar temperatures and reduced latitudinal gradients relative to the Holocene. These features represent a challenge for most climate models, implying either higher-than-predicted climate sensitivity to atmospheric CO 2 or systematic biases or misinterpretations in proxy data. Here, we present a reconstruction of marine temperatures at polar (> 80 •) and middle (∼ 40 •) paleolatitudes during the Early Jurassic (∼ 180 Myr ago) based on the clumped isotope (47) and oxygen isotope (δ 18 O c) analyses of shallow buried pristine mollusc shells. Reconstructed calcification temperatures range from ∼ 8 to ∼ 18 • C in the Toarcian Arctic and from ∼ 24 to ∼ 28 • C in Pliensbachian midpaleolatitudes. These polar temperatures were ∼ 10-20 • C higher than present along with reduced latitudinal gradients. Reconstructed seawater oxygen isotope values (δ 18 O w) of −1.5 ‰ to 0.5 ‰ VSMOW and of −5 ‰ to −2.5 ‰ VS-MOW at middle and polar paleolatitudes, respectively, point to a significant freshwater contribution in Arctic regions. These data highlight the risk of assuming the same δ 18 O sw value for δ 18 O-derived temperature from different oceanic regions. These findings provide critical new constraints for model simulations of Jurassic temperatures and δ 18 O sw values and suggest that high climate sensitivity has been a hallmark of greenhouse climates for at least 180 Myr.
Low-latitude seasonality of Cretaceous temperatures in warm and cold episodes
Nature, 2005
The Cretaceous period is generally considered to have been a time of warm climate 1-6 . Evidence for cooler episodes exists, particularly in the early Cretaceous period 6-8 , but the timing and significance of these cool episodes are not well constrained. The seasonality of temperatures is important for constraining equator-to-pole temperature gradients and may indicate the presence of polar ice sheets; however, reconstructions of Cretaceous sea surface temperatures are predominantly based on the oxygen isotopic composition of planktonic foraminifera 1-4 that do not provide information about such intra-annual variations. Here we present intra-shell variations in d 18 O values of rudist bivalves (Hippuritoidea) from palaeolatitudes between 88 and 318 N, which record the evolution of the seasonality of Cretaceous sea surface temperatures in detail. We find high maximum temperatures (,35 to 37 8C) and relatively low seasonal variability (<12 8C) between 208 and 308 N during the warmer Cretaceous episodes. In contrast, during the cooler episodes our data show seasonal sea surface temperature variability of up to 18 8C near 258 N, comparable to the range found today. Such a large seasonal variability is compatible with the existence of polar ice sheets.
2003
Oxygen isotope data for Upper Turonian planktonic foraminifera at DSDP Site 511 (Falkland Plateau, 60^oS paleolatitude) exhibit an ˜ 2 ppm excursion to values as low as -4.66 ppm (PDB) coincident with the warmest tropical temperature estimates yet obtained for the open ocean. The lowest planktonic foraminifer δ18O values suggest that the upper ocean was as warm as 30-32^oC. This is an extraordinary temperature for 60^oS latitude but is consistent with temperatures estimated from apparently coeval mollusk δ18O from nearby James Ross Island (65^oS paleolatitude). Glassy textural preservation, a well-defined depth distribution in Site 511 planktonics, low sediment burial temperature (˜ 32^oC), and lack of evidence of highly depleted pore waters argue against diagenesis (even solid-state diffusion) as the cause of the very depleted planktonic values. The lack of change in benthic foraminifer d18O suggests brackish water capping as the mechanism for the low planktonic δ18O values. However, mixing ratio calculations show that the amount of freshwater required to produce a 2 ppm shift in ambient water would drive a 7 psu decrease in salinity. The abundance and diversity of planktonic foraminifera and nannofossils, high planktonic:benthic ratios and the appearance of keeled foraminifera argue against lower-than-normal marine salinities. Isotope calculations and climate models indicate that we cannot call upon more depleted freshwater δ18O to explain this record. Without more late Turonian data, especially from outside the South Atlantic basin, we can currently only speculate on possible causes of this paradoxical record from the core of the Cretaceous greenhouse.
Geology, 2003
The middle Cretaceous (125-88 Ma) greenhouse world was characterized by high atmospheric CO 2 levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both ␦ 18 O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on ␦ 18 O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the ␦ 18 O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., TEX 86 [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The TEX 86 proxy indicates that tropical SSTs in the proto-North Atlantic were at 32-36 ؇C during the early Albian and late Cenomanian-early Turonian. This finding agrees with SST estimates based on ␦ 18 O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX 86 proxy indicates cooler SSTs (27-32 ؇C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on ␦ 18 O paleothermometry.
Earth and Planetary Science Letters, 2013
We apply the carbonate clumped isotope thermometer (D 47) to macrofossils from the Baculites compressus ($ 73.5 Ma) and the Hoploscaphites nebrascensis ($ 67 Ma) ammonite zones of the Western Interior Seaway (WIS) of North America, and nearby coeval terrestrial and open marine environments. The carbonate clumped isotope thermometer is based on a single-phase isotope exchange equilibrium that promotes the 'clumping' of two heavy isotopes together within a single carbonate molecule as temperature decreases. Due to the thermometer's isotopic independence from water, coupled measurements of D 47 and the bulk oxygen isotopic composition of a carbonate (d 18 O c) enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew. Before applying the technique to the aragonite shells of fossil marine organisms (mostly ammonites, but also some gastropods, bivalves, and one belemnite), we measure the clumped isotopic composition of modern nautilus and cuttlefish, two of the nearest living relatives to the Cretaceous ammonites. Modern cephalopods exhibit disequilibrium isotope effects with respect to D 47 , but not d 18 O c , therefore a simple correctional scheme is applied to the Late Cretaceous macrofossil data before reconstructing paleotemperatures. Diagenesis is also assessed by visual preservation and previously measured Sr concentrations (Cochran et al., 2003). Temperatures reconstructed for the Late Cretaceous Western Interior Seaway range from 16.4 7 3.5 1C for an offshore Interior Seaway environment from the H. nebrascensis zone to 24.2 7 0.4 1C for the B. compressus ammonite zone. The seaway itself has an isotopic composition of approximately À 1% (relative to VSMOW), the expectation for an ice-free global ocean average, while a nearby freshwater environment has an isotopic composition approaching À 20%. We compare the attributes of the reconstructed climate to predictions based on Late Cretaceous climate models and previous reconstructions of the seaway, and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs. Finally, our clumped isotope data are consistent with cooling between the Late Campanian and Maastrichtian, as also seen in benthic foraminfera d 18 O.
Evolving ideas about the Cretaceous climate and ocean circulation
Cretaceous Research, 2008
The Cretaceous is a special episode in the history of the Earth named for a unique rock type, chalk. Chalk is similar to modern deep-sea calcareous ooze and its deposition in epicontinental seas occurred as these areas became an integral part of the ocean. The shelf-break fronts that today separate inshore from openocean waters cannot have existed during the Late Cretaceous probably because the higher sea level brought the base of the wind-mixed Ekman layer above the sea floor on the continental margins. A second peculiarity of the Cretaceous is its warm equable climate. Tropical and polar temperatures were warmer than today. Meridional and ocean-continent temperature gradients were lower. The warmer climate was a reflection of higher atmospheric levels of greenhouse gasses, CO 2 and possibly CH 4 , reinforced by higher water vapor content in response to the warmer temperatures. Most of the additional energy involved in the meridional heat transport system was transported as latent heat of vaporization of H 2 0 by the atmosphere. Poleward heat transport may have been as much as 1 Petawatt (20%) greater than it is today. C 3 plants provided for more efficient energy transport into the interior of the continents. Circulation of the Cretaceous ocean may have been very different from that of today. It is impossible for large areas of the modern ocean to become anoxic, but episodes of local anoxia occurred during the earlier Cretaceous and became regional to global during the middle of the Cretaceous. The present ocean structure depends on constant wind systems, which in turn depend on stability of the atmospheric pressure systems forced by polar ice. During most of the Cretaceous the polar regions were ice free. Without polar ice there were seasonal reversals of the high-latitude atmospheric pressure systems, resulting in disruption of the mid-and high latitude wind systems. Without constant mid-latitude westerly winds, there would be no subtropical and polar fronts in the ocean, no well-developed ocean pycnocline, and no tropical subtropical gyres dominating ocean circulation. Instead the ocean circulation would be accomplished through mesoscale eddies which could carry warmth to the polar regions. Greater knowledge and understanding of the Cretaceous is critical for learning how the climate system operates when one or both polar regions are ice free.