BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 37 
than is implied in such a computation, for the rate of renewal is very different in different 
parts of the Sound. The more central portion of the stream would enter to a much 
greater distance than that close to shore, while the waters contained in various depres- 
sions of the bottom (if we may judge from temperature considerations) are probably 
renewed at a comparatively slow rate. 
In Buzzards Bay the change is in all probability much more slow, owing to the fact 
that this body of water communicates with the ocean at one end only, and that its mouth 
is very narrow in proportion to the total area of the Bay. Here there plainly can be no 
such continuous displacement in one direction as was found to occur in Vineyard Sound, 
and the renewal must be effected entirely through the mixture of waters resulting from 
the ebb and flow of the tide. The amplitude of the tides is, however, considerably 
greater in the Bay than in the Sound. Since the mean depth of the former is much less 
than that of the latter, a proportionally larger degree of change must result from this 
cause. The mean depth of Buzzards Bay, as computed from the 91 soundings indicated 
upon the chart contained in the Atlantic Coast Pilot, part m1, is a little over 41 feet. 
The average rise and fall of the tide in Buzzards Bay is about 4 feet. Thus the amount 
of water brought in by the flood tide is equal to about one-tenth of the total volume 
already contained inthe Bay. To what degree this ocean water mixes with that already 
present in the Bay, and, conversely, what proportion of the water which leaves the Bay 
on the ebb tide consists of that which entered on the previous flood, would be impossible 
to determine even approximately. Assuming that as much as one-half of this remains 
behind, which seems an extreme supposition, then the entire Bay would require 20 tides 
er 10 days to effect a complete renewal. On the whole, therefore, it seems likely that 
the average rate at which the water is renewed in Buzzards Bay is not over half that 
which obtains in Vineyard Sound. 
It is obvious, however, that this renewal of water would take place at quite different 
rates in different parts of the Bay. Near the mouth the change is probably much more 
rapid than the above figures would imply, while at its head the renewal of water is 
probably far slower. Likewise the surface water is probably changed at a much more 
rapid rate than are the lower strata. It must be remembered, also, that it is not pure 
ocean water which enters either the Bay or the Sound, but coastal water, which has been 
contaminated during previous ebb tides. Nevertheless, even such crude estimates 
may be of service in showing the relative stagnancy of the two bodies of water under 
consideration. 
A feature of great importance in determining the character of the local littoral fauna 
and flora is the slight amplitude of the tides throughout the entire region. A table will 
best illustrate the amplitude of the mean, spring, and neap tidesat 11 representative points. 
aan we | 
Mean. | Spring. Neap. || | Mean. Spring. | Neap. 
ts | | ees [ae 4 ast | 
Feet. Feet. | Feet. Feet. Feet Feel. 
BNAECHOOS ¢— 9 01g vs creme? Aat peak 3-0 || Tarpaulin Cove . ques a oeiertte 23 2.8 | 1.7 
Newrediord...o...c cnet sues 4.2 5.2 3-1 || Vineyard Haven..............| 1.7 i | 1.2 
Woods Hole (Bay side)........ ae 5.0 3-0 Woods Hole (Sound side) .....| I. 7 2.1 1.2 
Mouth of Bay (Westport)..... 34 3-8 2.3 | Edgartown a... esate aeaeet 2.0 2.4 | i. 5 
COTS IAS CS orl ee 3.5 4:3 2.6 1 Nantucket Harbor.......... 3. 3-8 | ae 
(CPN 18 C2: (a ee ea 3 3-0 3-7 2.2 | 
