A plate tectonic mechanism for methane hydrate release along subduction zones

Reconciliation of marine and terrestrial carbon isotope excursions based on changing atmospheric CO2 levels

“…G lobally correlated, negative excursions in carbon isotope (d 13 C) values measured in marine and terrestrial substrates throughout the Phanerozoic indicate episodic, massive additions of isotopically depleted carbon to the oceanatmosphere system [1][2][3][4][5][6][7][8][9][10] . These events not only changed the carbon isotope composition of atmospheric carbon dioxide (d 13 C CO2 ), but also raised pCO 2 concentrations (for example, ref .…”

“…One complicating factor is that the magnitude of the CIE is characteristically larger when measured in terrestrial versus marine substrates by up to several per mil [6][7][8][9]11,15 . Workers have argued that larger-magnitude negative excursions recorded in terrestrial substrates reflect increased humidity or precipitation 6,7 based on the increased carbon isotope fractionation that modern land plants demonstrate in response to these environmental factors.…”

Prediction of atmospheric δ¹³CO₂ using fossil plant tissues

“…[23] Reconstruction of paleo-d 13 CO 2 using d 13 C measurements of plant tissues has been a central part of many carbon cycling and paleoclimate reconstructions [e.g., Jahren, 2000, 2002;Hasegawa et al, 2003;Jahren, 2002;Jahren et al, 2001Jahren et al, , 2005Strauss and Peters-Kottig, 2003]. Perhaps more widely used is the practice of inferring soil d 13 CO 2 from soil organic matter d 13 C in order to ultimately solve for atmospheric pCO 2 level, temperature, or other fundamental climate attribute [e.g., Cerling, 1991Cerling, , 1992Ekart et al, 1999;Jahren et al, 2004a;Krull and Retallack, 2000;Ludvigson et al, 1998;Mora et al, 1991Mora et al, , 1996Nordt et al, 2002;Tabor et al, 2004;Yapp, 2004; Yapp and Poths, 1996].…”

“…We contend that a substrate comprising the contribution of multiple species and many individual plants is available within a few cubic centimeters of many terrestrial rocks and comprises the optimal substrate for d 13 C a reconstruction. In order to explore substrates that reflect little or no diagenesis, researchers have also explored the isolation and analysis of many types of specific structures and compounds exclusively associated with terrestrial land plants, including wood [Gröcke et al, 1999;van Bergen and Poole, 2002], cuticle Jahren, 2000, 2002;Jahren, 2002;Jahren et al, 2001Jahren et al, , 2005van Bergen et al, 1995], pollen [Jahren, 2004;Amundson et al, 1997;Hemming, 2000, 2001], rbcL gene DNA [Jahren et al, 2004b[Jahren et al, , 2006, and general ''biomarkers'' [Briggs et al, 2000;Pancost and Boot, 2004]. In each case, discrimination imparted during synthesis of specific plant components must be considered.…”

“…This led us to hypothesize that the d 13 C p value of fossil plant tissue could be used to reconstruct the d 13 C p value of the atmosphere, provided that the analytical substrate included the contribution of many species across various states of ecological functioning and could be meaningfully assessed for diagenetic alteration Jahren, 2000, 2002;Jahren, 2002;Jahren et al, 2001Jahren et al, , 2005. This approach has been questioned at several levels ranging from the possibility of nonlinearity at more extreme values of d 13 C p and d 13 C a [Gröcke, 2002] to the possibility of variable (c i /c a ) under changing environmental conditions at both ecological and evolutionary timescales .…”