Data from over 3 years of bottom pressure recording together with Geos
at altimetry and the Fine Resolution Antarctic Model numerical ocean m
odel have been used to investigate the temporal variability of the Ant
arctic Circumpolar Current between Amsterdam and Kerguelen islands in
the southern Indian Ocean. An upper limit to the standard deviation of
the variability in transport derived from pressure differences has be
en calculated to be 10-15 Sv, subject to an assumption of barotropic f
low dominating the variability and after the application of a 31-day l
ow-pass filter. This is slightly larger than the variability obtained
in a similar experiment at the Drake Passage a decade ago. Although th
e seasonal cycles in pressure difference and in sea surface height dif
ference measured by altimetry are different each year, their means are
consistent with the presence of a semiannual component with an amplit
ude in terms of (assumed barotropic) transport of the order of 5 Sv, w
hich is comparable to the Drake Passage findings. In addition, the pre
ssure difference data contain a large, quasistationary annual componen
t of amplitude of approximately 5 mbar, a possible source of which is
different seasonal steric fluctuations at the two sites. Insofar as th
e bottom recorder data can be considered ground truth for the altimetr
y, results from the different techniques show some features in common,
although significant differences between data sets remain, for which
possible explanations are offered. It is concluded that when they are
used for monitoring transport fluctuations, bottom pressure recorders
should be accompanied by inverted echo sounders and comprehensive hydr
ographic measurements.