|Reconstruction of vertical temperature gradients in past oceans - Proxy data from the Hauterivian-early Barremian (Early Cretaceous) of the Boreal Realm|Mutterlose, J.; Malkoc, M.; Schouten, S.; Sinninghe Damsté, J.S. (2012). Reconstruction of vertical temperature gradients in past oceans - Proxy data from the Hauterivian-early Barremian (Early Cretaceous) of the Boreal Realm. Palaeogeogr. Palaeoclimatol. Palaeoecol. 363: 135-143. dx.doi.org/10.1016/j.palaeo.2012.09.006
In: Palaeogeography, Palaeoclimatology, Palaeoecology. Elsevier: Amsterdam; Tokyo; Oxford; New York. ISSN 0031-0182; e-ISSN 1872-616X, meer
TEX86; Stable isotopes; Belemnites; Hauterivian; Boreal Realm;Palaeotemperature
|Auteurs|| || Top |
- Mutterlose, J.
- Malkoc, M.
- Schouten, S., meer
- Sinninghe Damsté, J.S., meer
A total of 25 mudstone samples from two sections in northwest Germany and northeast England (palaeolatitude similar to 40 degrees N), respectively, of Hauterivian and early Barremian age were analysed using TEX86 palaeothermometry. In addition, the stable isotope ratio (delta O-18, delta C-13) and trace element content (Mg, Sr, Fe, and Mn) of 138 belemnite guards from the same two outcrops were determined to reconstruct past sea water temperatures.
The TEX86 based sea surface temperatures were constantly warm (24-26 degrees C) throughout the entire Hauterivian for both sections and even warmer for the early Barremian (27-30 degrees C). Stable water temperatures prevailed over a period of similar to 6.4 Ma in the southernmost part of the Boreal Realm. These findings clearly support the view of warm equable conditions for the Hauterivian at least for mid latitudinal settings. A constant off-set between higher TEX86-derived temperatures and lower delta O-18(Bel)-derived temperatures was observed. This may be explained by either increased sea water salinities, a deep dwelling habitat of belemnites or a combination of both. A by 3 parts per thousand higher salinity of the sea water below the thermocline, which would at least partly explain the by similar to 2 parts per thousand too positive delta O-18(Bel) cannot be ruled out in these epicontinental settings. A habitat of the belemnites below the thermocline in perhaps 50-100 m water depth may have contributed to the positive delta O-18(Bel) data as well. The temperature difference between the TEX86 and the delta O-18(Bel) might therefore reflect a vertical temperature gradient of the water column of 4-5 degrees C and a salinity of the subsurface waters of 38 parts per thousand.