Risti Endriani Arhatin

Variability of satellite-derived sea surface height anomaly, and its relationship with Bigeye tuna (Thunnus obesus) catch in the Eastern Indian Ocean

Abstract We analyzed the variability of sea surface height anomaly (SSHA), and its relationship with Bigeye tuna catch in the eastern Indian Ocean (EIO) off of Java Island (Indonesia). Both time series of SSHA and Bigeye tuna HR show dominant signals corresponding to the annual and inter-annual variability. During the southeast monsoon the wind blows along southern coast of Java and produces coastal upwelling. This causes sea level to drop due to an offshore Ekman transport, and thermocline becomes shallower. During El Niño and Indian Ocean Dipole (IOD) positive phase, upwelling is more intense and a large cold eddy forms in the EIO off Java. Generally, Bigeye tuna HR tends to increase during upwelling seasons and becomes even higher during El Niño and the positive phase of the IOD. The increased Bigeye tuna HR during the southeast monsoon, El Niño and the IOD positive phase can be attributed to the shallower thermocline depth and the enhancement of biological productivity due to development of eddies and strong upwelling in the EIO. The spatial distribution of SSHA indicates that Bigeye tuna catches are abundant in the frontal regions between cold and warm eddies.

An assessment of a coastal altimetry data product in the Indonesian Waters

We analyzed the percentage of valid coastal altimetry Jason-2 X-TRACK-SLA data by Center for Topographic Studies in Sea and Hydrosphere (CTOH) and the waveforms from the Sensor Geophysical Data Record (SDGR) that are distributed by NOAA National Ocean Data Center around the Indonesian waters. In general, the percentage of valid data after the first point of the shoreline is greater than 90%. The percentage of valid data in steeper waters (86%) is higher than sloping waters (34%). The waveform types formed in coastal waters are peaky and Brown. However, spatially there is a difference where in a steep coast at a distance of > 5 km from the coastline the type of waveform is identified Brown, while on the sloping coast the brown type is found at a distance > 10 km. The SLA time series indicate seasonal variations in which the SLA is negative during the Southeast Monsoon (May-October) and positive during Northwest Monsoon (November-April).

SEASONAL VARIABILITY OF LIGHT ABSORPTION COEFFICIENT OF SURFACE WATER

Absorption coefficient measurement can be use d in estimat ing water quality, op t ical characteristic of water column, and marine bio-optical models. The purposes of this research were to determine values and variability of sea surface absorption coefficient in the northeastern Gulf of Mexico (NEGOM) based on various seasons. The data were collected in spring, summer, and fall seasons in 1999-2000 with AC-9 instrument. The spatial distribution of absorption coefficient showed that relatively high values were generally found along the run off Missisippi, Mobile, Chochawati, Escambia, Apalachicola, and Suwannee rivers, as well as Tampa Bay. Meanwhile, relatively low values were found in offshore region. This pattern followed the distribution pattern of chlorophyll and CDOM. Based on the local region comparison of spectral average value of absorption coefficient, we found a significant difference (α = 95%) among regions with the highest value in the run off of the Mississippi and Mobile rivers, and the lowest value in the offshore region. Comparison of spectral average value of absorption coefficient among seasons at the three primary wavelengths (blue=440 nm, green=510 nm, and red=676 nm) also showed a significant difference (α = 95%) with the highest value during the summer 1999 (Su-99) and the lowest value during the spring of 2000 (Sp-00). Absorption coefficient values were influenced by oceanographic factors that varied in every season such as wind, surface currents, upwelling, the location and speed of the Loop Current, and the river discharge of fresh water into the NEGOM. Keywords: absorption coefficient, seasons, chlorophyll, CDOM, northeastern Gulf of Mexico