between seawater and basaltic ocean crust. However, estimates of the element
fluxes involved in these processes are uncertain, mainly because representative
sampling in these remote environments is difficult and expensive. The flux
estimates are based on a few studies at individual sites on the East Pacific and
Mid-Atlantic ridges (Fig. 6.16). Global fluxes have been calculated from these
sites, using various geophysical and geochemical approaches. A major problem
however, still to be resolved, is a rigorous quantification of the amount of
hydrothermal activity occurring at high temperatures near the ridge axis, versus
lower temperature circulation on the ridge flanks (Fig. 6.14 & Table 6.5). This
is important, because temperature affects the degree, rate and even direction of
some chemical reactions. Despite these problems, for some elements the direc-
tion of the fluxes agree from site to site allowing construction of tentative global
fluxes (Table 6.2). We should, however, note that the magnitudes of the fluxes in
Table 6.2 are uncertain.
In the following section we describe the effects of hydrothermal activity
on major ions in the oceans: the effects on minor components in the oceans are
discussed in Sections 6.5.2 and 6.5.5.The Oceans 2110 °30 °30 °60 °S60 °NCarlsbergRidge
Red
Sea
iR
dg
eChil
eR
iseLau/Valu FAN. Fiji BasinWoodlark
BasinManus BasinMarina TroughOkinawa
TroughEscanaba
Trough
EPR 10–21°N
EPR 3.5°SSoutheast
Indian RidgeEndeavor
CleftTagRainbowLucky
StrikeSteinaholl
AzoresRidge120 ° 150 ° 180 ° 150 ° 120 ° 90 ° 60 ° 30 ° 0 ° 30 ° 60 ° 90 °KaireiGuyamus
BasinExplorer, Juan de
Fuca, and Gorda RidgesPacif
icAntarc
ticRidg
eaE
ts
Pacific
Rise
Galapagos
EPR
17–19°SEast Scotia
RidgeMid
AtlanticSnake Pit/MarkBroken SpurAsal Rift
Central
Indian
RidgeSou
thwest
Indi
an
RidgeKnipovichGakkol RidgeEdmondMid-ocean Ridge
Subduction zone
Hydrothermal vent sitesFig. 6.16Location of known mid-ocean ridge hydrothermal systems in the oceans. After Baker et al. (1995).