Throughflow

Abstract: Simultaneous observations of rapid preferential flow through macropores and isotopically “Old” water displacement remain unresolved in the Maimai (M8) catchment. Continuous, three-dimensional soil moisture energy conditions were monitored in two discrete catchment positions for a series of storm events in 1987. Tensiometric response was related to the soil water characteristic curve, hillslope throughflow, and total catchment runoff. For events yielding ≪2 mm hr−1 peak runoff, near-stream valley bottom groundwater systems discharged water volumes sufficient to account for storm period streamflow. This process was assisted by regular low ( 2 mm hr−1 peak storm flow, hillslope hollow drainage into steeply sloping first-order channels dominated old water production and most of the catchment storm flow. Highly transient macropore-driven processes of crack infiltration (bypass flow), slope water table development, and lateral pipe flow enabled large volumes of stored water to be delivered to the first-order channel bank at the appropriate time to satisfy catchment storm flow volumes and water isotopic and chemical composition.

Abstract: THE physical structure of the Pacific and Indian oceans is substantially affected by the inter-ocean transport of excess fresh water from the North Pacific Ocean through the Indonesian seas1,2. The efficiency of this transport is an important regulator of the meridional overturning of these oceans1,2, and hence perhaps of the global thermohaline circulation3; in addition, the seepage of warm water out of the Pacific affects the volume of the western Pacific warm pool, and thus may influence EI Nino events24. But the sources, pathways and physical properties of the Indonesian throughflow are not well enough characterized to allow its influence on ocean circulation and the climate system to be quantified. Here we report salinity, temperature and chemical-tracer data from the Indonesian seas which show that the throughflow is dominated by two components: one of low-salinity, well ventilated North Pacific water through the upper thermocline of the Makassar Strait, and the other of more saline South Pacific water through the lower thermocline of the eastern Indonesian seas. Seasonal (monosonal) variations in the ratio of these components, perhaps modulated by EI Nino conditions, imply the existence of potentially important variable feedbacks to the ocean circulation and climate system.

Abstract: The expendable bathythermograph (XBT) line Fremantle-Sunda Strait transects the eastern Indian Ocean between northwestern Australia and Java. It was established in 1983 with low-density sampling and upgraded to a frequently repeated line (>18 times per year) in 1987 to monitor currents. The observations during 1983 to 1994 are described and related to the field of wind stress. Variation of thermal structure shows a rich mixture of annual, semiannual, and interannual timescales. Empirical orthogonal function (EOF) analysis of anomalies of sea surface temperature (SST), dynamic height, and depth of the 20°C isotherm D 20 identifies two distinctive signals. The El Nino - Southern Oscillation (ENSO) signal (EOF 1) appears throughout the region and is strongest off the coast of Australia. A modulation of the annual signal (EOF 2) appears off the coast of Java. EOF 2 has a shorter timescale than the ENSO signal, and its temporal coefficients are correlated to zonal winds over the equatorial Indian Ocean. For both EOFs, anomalously low SST and dynamic height occur at the same time as anomalously shallow D 20 and vice versa for opposite anomalies. The XBT data are used with a climatological temperature-salinity relationship to calculate net, relative (0/400 dbar) geostrophic transports T through the section. For long timescales, T is representative of Indonesian throughflow. The variations associated with ENSO show a maximum during the La Nina of 1988-1989 and minima during the El Ninos of 1986-1987 and 1991-1994. The peak-to-trough amplitude of the ENSO signal is 5 Sv. The ENSO signal in throughflow is discussed in terms of earlier studies. For the shorter timescales, T is representative of currents from the Indian Ocean flowing in and out of the region between northwestern Australia and Indonesia, changing the volume of upper layer water stored there. Associated with EOF 2, a sharp peak in westward transport developed during May to October 1994.