Old carbon reservoirs were not important in the deglacial methane budget.

Permafrost and methane hydrates are large, climate-sensitive old carbon reservoirs that have the potential to emit large quantities of methane, a potent greenhouse gas, as the Earth continues to warm. We present ice core isotopic measurements of methane (Δ14C, δ13C, and δD) from the last deglaciation, which is a partial analog for modern warming. Our results show that methane emissions from old carbon reservoirs in response to deglacial warming were small (<19 teragrams of methane per year, 95% confidence interval) and argue against similar methane emissions in response to future warming. Our results also indicate that methane emissions from biomass burning in the pre-Industrial Holocene were 22 to 56 teragrams of methane per year (95% confidence interval), which is comparable to today.

The organization of a tunicate heart.

Cardiac myoepithelial cells contain three myofibrils adjacent to the lumen. Zonula adhaerentes connect myofibrillar ends; desomosomes and peg-in-socket connections occur laterally with zonulae occludenfes at the pericardial border. Conduction and contraction are vertebrate cardiac muscle type. T-tubules are absent ; atypical sarcoplasmic vesicles run between myofibrils and beneath the sarcoplasmic membrane. Multivesiculate vacuoles, on cytoplasmic lobes protruding into the lumen from sarcomeric positions, induce reversal of heartbeat by a secretory feedback mechanism. Auto-UV-fluorescent dense bodies aooarentlv assemble thick and thin filaments. Both pericardial cavity borders are pinocytotic. Exaggerated interdigitation of adjacent plasma membranes and thick basement membrane of pericardial cells contribute mechanically to heart action.