22
CORDON A. RILEY
The possibility that the observed seasonal change in organic carbon
resulted from in s i t u biological events can be ruled out fairly quickly.
The total seasonal increase is of the order of 100 g C/m2 of sea surface,
which is equal to or greater than net phytoplankton production at the
surface. The observed increase therefore cannot be accounted for in
terms of sinking of organic matter from the surface, and even if it
could be, the seasonal cycle of phytoplankton production is not of a
sort that would lead to a short winter maximum.
The other possibility of in s i t u processes is conversion of part of
the dissolved organic matter to particulate matter. Later information
will suggest that such transformations might be possible, but for them
to occur on a seasonal basis in an essentially seasonless deep ocean seems
unlikely. Moreover, this would not supply a reasonable explanation for
the increase in organic phosphorus noted by McGill et al., which included
dissolved and particulate fractions.
The alternative to in s i t u changes is a seasonal movement of water
of different composition through the area, and this must be a generalized
movement from surface to bottom rather than an intrusion of particular
water masses.
The only presently known source of water with a sufficiently high
content of organic carbon to account for the observed winter maximum
is the area to the north, where Menzel and Ryther (1964) reported fairly
large concentrations in winter and spring just north and south of the
Gulf Stream. The concomitant winter increase in salinity in Bermuda
waters is in accordance with such movement, for there is a slight but
significant north-south gradient in salinity in the great water mass
lying between the Gulf Stream and the tropics.
Direct evidence on current movements is fragmentary. This is not
an area where estimates of deep currents by geostrophic rrethods are
simple and reliable, and no direct current measurements have been
made on a year around basis. Even information on surface currents is
scanty. Day and Webster (1965) described a series of current observations obtained with a buoy moored at about 28"N 65"W in which
currents were recorded continuously from October 10, 1962 to January
27, 1963. The long term drift at this station, located some 250 miles
south of Bermuda, was toward the north during the first part of this
period, averaging about 8 km/day. I n early January the current
veered to the east and then to the south. During the last two weeks
of the observation period the water was flowing south at an average
speed of 14 km/day. If currents of this magnitude prevailed over a
considerable area, they could move surface water from the vicinity of
the Gulf Stream to the latitude of Bermuda in about a month.
CORDON A. RILEY
The possibility that the observed seasonal change in organic carbon
resulted from in s i t u biological events can be ruled out fairly quickly.
The total seasonal increase is of the order of 100 g C/m2 of sea surface,
which is equal to or greater than net phytoplankton production at the
surface. The observed increase therefore cannot be accounted for in
terms of sinking of organic matter from the surface, and even if it
could be, the seasonal cycle of phytoplankton production is not of a
sort that would lead to a short winter maximum.
The other possibility of in s i t u processes is conversion of part of
the dissolved organic matter to particulate matter. Later information
will suggest that such transformations might be possible, but for them
to occur on a seasonal basis in an essentially seasonless deep ocean seems
unlikely. Moreover, this would not supply a reasonable explanation for
the increase in organic phosphorus noted by McGill et al., which included
dissolved and particulate fractions.
The alternative to in s i t u changes is a seasonal movement of water
of different composition through the area, and this must be a generalized
movement from surface to bottom rather than an intrusion of particular
water masses.
The only presently known source of water with a sufficiently high
content of organic carbon to account for the observed winter maximum
is the area to the north, where Menzel and Ryther (1964) reported fairly
large concentrations in winter and spring just north and south of the
Gulf Stream. The concomitant winter increase in salinity in Bermuda
waters is in accordance with such movement, for there is a slight but
significant north-south gradient in salinity in the great water mass
lying between the Gulf Stream and the tropics.
Direct evidence on current movements is fragmentary. This is not
an area where estimates of deep currents by geostrophic rrethods are
simple and reliable, and no direct current measurements have been
made on a year around basis. Even information on surface currents is
scanty. Day and Webster (1965) described a series of current observations obtained with a buoy moored at about 28"N 65"W in which
currents were recorded continuously from October 10, 1962 to January
27, 1963. The long term drift at this station, located some 250 miles
south of Bermuda, was toward the north during the first part of this
period, averaging about 8 km/day. I n early January the current
veered to the east and then to the south. During the last two weeks
of the observation period the water was flowing south at an average
speed of 14 km/day. If currents of this magnitude prevailed over a
considerable area, they could move surface water from the vicinity of
the Gulf Stream to the latitude of Bermuda in about a month.