On the calculation of total heat, salt and tracer fluxes from ocean hydrothermal events

Total heat, salt, and other tracer masses released during a hydrothermal ev ent are shown to be proportional to, but not necessarily equal to, volume i ntegrals of resulting water column anomalies. Proportionality coefficients depend on anomaly definition, on background hydrographic and tracer profile s, on expansion coefficients of the equation of state at an appropriate pre ssure, and on tracer to heat anomaly ratios at the venting source. For Gord a Ridge event plumes, which are described in other papers of this issue, vo lume integrals of conventionally defined heat anomalies underestimate actua l released heat by a factor of 2.4 if the discharge is not anomalously sali ne. Under certain combinations of hydrographic and source anomaly condition s, not unlike those found on the East Pacific Rise at 10 degrees N, the app arent total heat released during an event can be deceivingly zero. This ana lysis also establishes a linear relationship between the ratio of tracer an omaly to heat anomaly at any point in the plume to the same ratio at the so urce. One consequence is that the ratio of anomalous He-3 to heat in Gorda Ridge event plumes is approximately 2.4 larger in the water column than it is at the source. Results are independent of the entrainment process involv ed in event plume formation, and they are shown to hold true even for backg round hydrographic profiles that do not vary linearly with depth. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.