The winter of 1992 was the coldest on record in New Zealand since the
1940s. Temperatures in New Zealand were as much as 3 degrees C below a
verage, with heavy rain and unusual snow. The oceanic surface layer in
the southwest Pacific was also anomalously cold over the same period.
A World Ocean Circulation Experiment (WOCE) hydrographic section (P14
C) between Auckland and Fiji during September 1992 found cold sea surf
ace temperatures and deep mixed layers near New Zealand when compared
to 8 years of high-resolution expendable bathy thermograph (XBT) tempe
rature measurements collected along the same transect. High nutrient a
nd low dissolved oxygen concentrations in the surface layer indicated
recent entrainment of thermocline waters. The Auckland to Fiji XBT sec
tion is ope of three WOCE high-resolution XBT survey lines in the ''Ta
sman Box'' region, whose boundaries are Auckland-Fiji, Fiji-Brisbane a
nd Wellington-Sydney transects plus the Australian coast. Geostrophic
shear and transport were estimated from 10 realizations of the Tasman
Box during the period 1991-1993. The time series of geostrophic transp
ort shows that following a convergence in late 1991, early in 1992 the
re was a substantial divergence of mass in the upper waters, equivalen
t to a thinning of the warm water layer. The phase of this anomalous d
ivergence is matched to an observed amplification of the seasonal ocea
nic heat storage cycle in 1991-1992. The top 200-m average temperature
was warmer in the 1992 summer than in 1991 or 1993, but the winter of
1992 was the coldest of the 8-year record along the Auckland-Fiji lin
e. The divergence (thinning) of the warm water layer appears to have p
reconditioned the region for the exceptionally cold 1992 winter. The a
lternative, cool conditions from anomalous air-sea heat exchange cause
d by variability in the wind field, is considered unlikely as large fl
uctuations in heat loss are not observed in the air-sea flux data duri
ng this period. The severe weather conditions and anomalous ocean heat
transport are most likely related to the prolonged El Nino-Southern O
scillation episode that began in early 1991.