Biology Reference
In-Depth Information
forces the gravitational pull of the others, creating a tide powerful enough
to move nearly a quarter of the water volume of the bay. The smallest tide,
a
neap tide
, occurs in-between times, when the moon waxes or wanes to a
quarter, and when the gravitational pull of the sun and moon are not
aligned. The movements of the sun and moon across the seasons also in-
fluence tidal strength. Extreme high and low tides take place in the bay
from May through June, and from November through December.
As the tides turn, most of the water goes in and out, over and over; only
a relatively small portion is “new” water each time. “It's like a concertina—
you can squash it up and stretch it out again, and while things are moving
they're not really going anywhere,” says John Largier, an oceanographer
with UC Davis's Bodega Marine Lab.
Sea surface temperatures off the bay's Pacific shores, with red and yellow depict-
ing the warmest waters, blue the coldest, and green in-between. San Francisco Bay
often shoots a jet of warm, fresh surface water through the Golden Gate. At the
same time, local winds push California current waters in an arc (the yellow swirl),
west past the Farallon Islands, south toward Half Moon Bay, then north again to-
ward the Golden Gate. Cooler upwelled waters appear off Point Arena and Point
Reyes. (John Largier)
