Sea level change: a philosophical approach

Abstract

The present Cenozoic era is an 'icehouse' episode characterized by a low sea level. Since the beginning of the industrial revolution, the human race has been emitting greenhouse gases, increasing the global atmospheric temperature, and causing a rise in sea level. If emissions continue to increase at the present rate, average global temperatures may rise by 1.5 °C by the year 2050, accompanied by a rise of about 30 cm in sea level. However, the prediction of future climatic conditions and sea level is hampered by the difficulty in modelling the interactions between the lithosphere, kryosphere, biosphere and atmosphere; in addition, the buffering capacity of our planet is still poorly understood. As scientists cannot offer unambiguous answers to simple questions, sorcerer's apprentices fill in the gaps, presenting plans to save planet without inconveniencing us.The geological record can help us to learn about the regulation mechanisms of our planet, many of which are connected with or expressed as sea level changes. Global changes in sea level are either tectono-eustatic or glacioeustatic. Plate tectonic processes strongly control sea levels and climate in the long term. There is a strong feed-back mechanism between sea level and climate; both can influence and determine each other. Although high sea levels are a powerful climatic buffer, falling sea levels accelerate climatic accentuation, the growth of the polar ice caps and will hence amplify the drop in sea level. Important sources of fossil greenhouse gases are botanic CO2 production, CO2 released by volcanic activity, and water vapour. The latter is particularly important when the surface area of the sea increases during a rise in sea level ('maritime greenhouse effect'). A 'volcanogenic greenhouse effect' (release of volcanogenic CO2) is possibly not equally important, as intense volcanic activity may take place both during icehouse episodes as well as during greenhouse episodes. The hydrosphere, land vegetation and carbonate platforms are major CO2 buffers which may both take up and release CO2. CO2 can be released from the ocean due to changes in the pCO 2 caused by growth of coral reefs and by uptake of CO2-rich freshwater from karst provinces. Efficient sinks of CO2 are the weathering products of silicate rocks; long-term sinks are organic deposits caused by regional anoxic events which preferrably develop during sea level rises and highstands; and coal-bearing strata. Deposition of limestone also removes CO2 from the atmospherichydrospheric cycle at a long term. Biotic crises are often related to either sea-level lows or sea-level highs. Long-term sea-level lows, characteristic of glacial periods, indicate cooling as major cause of extinction. During verly long-lasting greenhouse episodes the sea level is very high, climate and circulation systems are stable and biotic crises often develop as a consequence of oxygen depletion. On land, niche-splitting, complex food web structures and general overspecialization of biota will occur. Whether the crisis is...

Effects of antecedent topography on reefal carbonate deposition: Early-Middle Miocene of the Adana Basin, S Turkey

“…Reef growth is effected by numerous controlling factors such as subsidence rate, climate, eustatic sea level changes, antecedent topography, substratum type, sediment input and grain-size, wave/current energy, water turbidity, temperature and salinity, aragonite saturation, atmospheric CO 2 , nutrient levels, carbonate producer type, and organic diversity (Heckel, 1972;Gö rür, 1979;Leeder, 1982;Boggs, 1987;Jones and Desrochers, 1992;Leinfelder and Seyfried, 1993;Prothero and Schwab, 1996;Leinfelder, 1997;Reinhold, 1999;Montaggioni, 2000, 2005Sanchez et al, 2002Brooks et al, 2003;Gischler and Hudson, 2004;Vennin et al, 2004;Bassant et al, 2005;Fournier et al, 2005). Changes in one or more factors may affect the others and shut-down reefal sedimentation.…”

The Frasnian–Famennian biotic crisis: How many (if any) bolide impacts?

“…The F-F ecosystem perturbations were probably superimposed on a prelude of climatic evolution from an ice-free to a glaciated world state. Thus, a model of more or less destabilized but unequivocally greenhouse conditions (Becker and House 1994), influenced by autocyclic productivity-controlled climatic-eustatic feedback, is the most acceptable (Buggisch 1991;Leinfelder and Seyfried 1993;Joachimski and Buggisch 1996). In addition, the key role of plant evolution in the Devonian that finally overshadowed tectonic effects in the atmospheric CO 2 balance and promoted Late Palaeozoic global cooling has recently been highlighted (e.g., Retallack 1997;Algeo and Scheckler 1998;Copper 1998).…”

“…Nevertheless, the several competing sources and negative feedback loops were probably active during the Late Devonian epoch. A rising sea level and intense degassing of volcanic CO 2 and H 2 O caused buffering of the greenhouse state ("maritime" and "volcanogenic" effects; Leinfelder and Seyfried 1993), especially that the absolute values of CO 2 levels remain vague (e.g. Liu and Schmitt 1996, p. 991).…”

Modelos Morfogenéticos E Tectônica Global: Reflexões Conciliatórias

“…Finalmente, não há ainda consenso sobre as respectivas responsabilidades assumidas pela tectônica (tectonoeustatismo) e pelas glaciações neocenozóicas (glacioeustatismo) na geração do eustatismo. Leinfelder & Seyfried (1993) demonstram o quanto é impossível isolar os seus respectivos papeis.…”

“…No primeiro caso, Leinfelder & Seyfried (1993) afirmaram que, "a longo prazo o processo da tectônica de placas controla fortemente os níveis marinhos e o clima". Em períodos de tempo menores, ocorrem importantes mecanismos interativos entre o nível do mar e o clima.…”