Temperature changes oceanic

Cutler KB, Edwards RL, Taylor FW, Cheng H, Adkins J, Gallup CD, Cutler PM, Btrrr GS, Chappell J, Bloom AL (2003) Rapid sea-level fall and deep-ocean temperature change since the last interglacial. Earth Planet Sci Lett, in press... 

However, the question must always be asked as to whether these processes could have taken place on the primordial Earth in its archaic state. The answer requires considerable fundamental consideration. Strictly speaking, most of the experiments carried out on prebiotic chemistry cannot be carried out under prebiotic conditions , since we do not know exactly what these were. In spite of the large amount of work done, physical parameters such as temperature, composition and pressure of the primeval atmosphere, extent and results of asteroid impacts, the nature of the Earth s surface, the state of the primeval ocean etc. have not so far been established or even extrapolated. It is not even sure that this will be possible in the future. In spite of these difficulties, attempts are being made to define and study the synthetic possibilities, on the basis of the assumed scenario on the primeval Earth. Thus, for example, in the case of the SPREAD process, we can assume that the surface at which the reactions occur could not have been an SH-containing thiosepharose, but a mineral structure of similar activity which could have carried out the necessary functions just as well. The separation of the copy of the matrix could have been driven by a periodic temperature change (e.g., diurnal variation). For his models, H. Kuhn has assumed that similar periodic processes are the driving force for some prebiotic reactions (see Sect. 8.3). 

Any of these data banks, those parts from the ice ages, can have their stable isotope ratios perturbed by the huge ice reserves which were removed from the sea and piled up on land, because the ice depletes the oceans in the light isotopes, and therefore significantly enriches the sea in the heavy isotopes, so that sea sediments and continental precipitation, rain and snow, reflect this perturbation as well as perturbations caused by temperature changes alone. 

A wide range of 5 °Si values from -0.8 to - -5.0%o have been reported for Precambrian cherts (Robert and Chaussidon 2006), much larger than for Phanerozoic cherts. These authors observed a positive correlation of 8 0 with 8 Si values, which they interpreted as reflecting temperature changes in the ocean from about 70°C 3.5 Ga to about 20°C 0.8 Ga years ago. 

Phytoplankton at the ocean surface maintain the fluidity of their cell membranes by altering their lipid (fat) composition when the temperature changes. When the ocean temperature is high, plankton synthesize relatively more 37 2 than 37 3.35... 

Below the thermocline, the temperature changes only little with depth. The temperature is a non-conservative property of seawater because adiabatic compression causes a slight increase in the in situ temperature measured at depth. For instance in the Mindanao Trench in the Pacific Ocean, the temperature at 8500 and 10,000 m is 2.23 and 2.48 °C, respectively. The term potential temperature is defined to be the temperature that the water parcel would have if raised adiabatically to the ocean surface. For the examples above, the potential temperatures are 1.22 and 1.16 °C, respectively. Potential temperature of seawater is a conservative index. 

Because the mean pH of the today s ocean surface layer is about 8.08 (with a range from 7.9-8.25) (Raven et al, 2005), oceanic NH3 can exist as a dissolved, non-protonated gas and, thus, it is available for gas exchange across the ocean/ atmosphere interface. For example, for a pH of 8.1, a water temperature of 25°C, and a salinity of 35, about 6% is available as dissolved NH3, [NH3], (Fig. 2.8). The NH3/NH4 equilibrium is very sensitive to changes of the pH and water temperature. Changes in salinity and pressure are comparably less important (Fig. 2.8). 

Figure 11 Vostok temperature changes from present-day values back to 420 kyr BP, estimated either AT s(spat) (in red) by the conventional approach based on the 6D profile alone (Petit et al., 1999) accounting correctly for the oceanic correction (see text), or A7 s(inv) (in green) from the inverse method based on the use of deuterium excess to account for moisture source changes (source Vimeux et al, 2002).

Figure 13 The influence of the source temperature on the isotopic content of the Antarctic precipitation. Line B corresponds to the observed present-day spatial slope between Dumont d UrviUe and Dome C expressed with respect to the temperature of snow formation (i.e., above the inversion layer). Line A represents the temporal slope assuming that the temperature change at the oceanic source is half of that at the Dome C site.

Bacastow R. B. (1996) The effect of temperature change of the warm surface waters of the oceans on atmospheric CO2. Global Biogeochem. Cycles 10, 319—334. 

A unique secondary complication for Sr/Ca is the potential influence of small changes in seawater Sr/Ca. Although spatial variability in seawater Sr/Ca in the present ocean is very small (<2%) (Brass and Turekian, 1974 de ViUiers et al., 1994), the small sensitivity of the coral Sr/Ca paleothermometer makes it sensitive to these variations. For example, an observed 2% variation in coralline Sr/Ca, which equates to the maximum seawater variation, is equivalent to between a 2 °C and 5 °C temperature change, depending on the slope of the calibration (see Section 6.14.8.2). In practice, it is likely that most locations do not experience variations of more than 0.5% in seawater Sr/Ca (de ViUiers et al., 1994), but on historical timescales it is at least possible that larger shifts might have taken place. 

---