Seasonal Ekman upwelling in the Southwest Sumba from INDESO Model

Southwest Sumba water is part of the Indonesian fisheries management region (WPP573). Marine fisheries resources are influenced by oceanographic phenomena such as an upwelling event. This study aims to describe characteristics of seasonal Ekman upwelling by analyzing oceanographic parameters from the validated INDESO model output (2008-2014). It shows that upwelling event in the study area occurs during the Southeast Monsoon period, which creates an Ekman drift of 0.26 Sv towards offshore. This transported water mass is then replaced by an upwelled vertical flow of sub-surface colder and nutrient-rich water at the velocity of the order of 10−4 m/s. Surface features of the upwelling event are seen from a minimum temperature (24.3 °C), sea level anomaly (0.34 m), but the maximum of chlorophyll-a (3.02 mg/m3). During this time, an uplifted isotherm of 25.5 °C is found from sub-surface to 10 m depth, but it is outcropped at the sea surface in the centre of upwelling area. Interestingly, during upwelling event, salinity stratification revealed an isohaline of 34.10 psu is much deeper at 40 m depth, and much fresher water mass from the Ombai Indonesian Throughflow water is dominant. Averaged temperature-based upwelling index between June-September is about 0.3 °C.

Influence of coastal upwelling on the surface current in the Bay of Bengal using HF radar and satellite observations

<p>Coastal Upwelling is a phenomenon in which cold and nutrient-enriched water from the Ekman layers reaches the surface enhancing the biological productivity of the upwelling region. In this work, an attempt is made to understand the influence of coastal upwelling on surface current variations during May 2018 to August 2018, when HF radar current observation (source: NIOT, India) is available. The wind-based Upwelling Index(UI<sub>wind</sub>) showed coastal upwelling throughout the study period. But the SST based upwelling index (UI<sub>sst</sub>) showed upwelling occurred only from May to the first week of June. Cross-shore components of HF radar-derived ocean surface current (CSSC)  showed strong similarity with UI<sub>sst</sub>. The first phase of upwelling from UI<sub>sst</sub> is observed to start on 5<sup>th</sup> May and lasts till 14<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km. Then, there is a break period for about three days and after that, the second phase of upwelling starts on 17<sup>th</sup> May and lasts till 25<sup>th</sup> May with a maximum peak on around 20<sup>th</sup> May, but this time the horizontal extension is ~100 km which is much larger than during the first phase. A strong positive (from coast to offshore) CSSC is observed to start on around 5<sup>th</sup> May and lasts till 13<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km, as observed from UIsst. A reversal of CSSC (towards coast) is noted on 14<sup>th</sup> May when the break of coastal upwelling is evident from UI<sub>sst</sub>. The CSSC then again started intensifying 15<sup>th</sup> May onwards and continued for ten days till 25<sup>th</sup> May, similar to UI<sub>sst</sub>.  The horizontal extension of the upwelling signature in the second phase of upwelling is ~70 km. Therefore, a 7-10 days of the coastal upwelling and its horizontal extension are identified in this study. This study suggests the use of high resolution (~6 km) HF radar current observation on the monitoring of coastal upwelling processes.</p>

Influence of coastal upwelling on micro-phytoplankton variability at Valparaíso Bay (~33ºS), Central Chile

In this work 10 years of data (1986-1996) from a fixed station located in the northern part of Valparaíso Bay (33º00’S; 71º35’W) were analysed to study the influence of coastal upwelling activity on the temporal variation of micro-phytoplankton (20-200 μm) and their relationship with oceanographic conditions. The upwelling activity at the bay was associated to semi-annual wind regime with an intensification of upwelling-favourable S-SW winds from September to March followed by a decrease and the occurrence of downwelling events from April to August. Oceanographic conditions showed the ascent of cold, nutrient-rich salty water in spring (September-November). However, during summertime under highest upwelling index, thermal stratification conditions were registered. This stratification might be associated to either the solar radiation or the presence of an upwelling shadow area in the bay. The upwelling period had the highest micro-phytoplankton abundance mainly dominated by diatoms. This period was associated with an increase in biomass and richness in the bay. Meanwhile during non-upwelling period —under homogenous conditions of temperature, salinity and nutrients— an increase in diversity (but low abundance and richness) associated to dinoflagellates and silicoflagellates was noted. Therefore, the results suggest the presence of a bi-modal regime of micro-phytoplankton in the bay in response to changes in oceanographic conditions related to local wind forcing and mixing/stratification.

Herbaria macroalgae as a proxy for historical upwelling trends in Central California

Planning for future ocean conditions requires historical data to establish more informed ecological baselines. To date, this process has been largely limited to instrument records and observations that begin around 1950. Here, we show how marine macroalgae specimens from herbaria repositories may document long-term ecosystem processes and extend historical information records into the nineteenth century. We tested the effect of drying and pressing six macroalgae species on amino acid, heavy metal and bulk stable isotope values over 1 year using modern and archived paper. We found historical paper composition did not consistently affect values. Certain species, however, had higher variability in particular metrics while others were more consistent. Multiple herbaria provided Gelidium (Rhodophyta) samples collected in southern Monterey Bay from 1878 to 2018. We examined environmental relationships and found δ 15 N correlated with the Bakun upwelling index, the productivity regime of this ecosystem, from 1946 to 2018. Then, we hindcasted the Bakun index using its derived relationship with Gelidium δ 15 N from 1878 to 1945. This hindcast provided new information, observing an upwelling decrease mid-century leading up to the well-known sardine fishery crash. Our case study suggests marine macroalgae from herbaria are an underused resource of the marine environment that precedes modern scientific data streams.

On the changes in the sea surface temperature in the Benguela upwelling region. Part 1: season cycle

Based on daily ocean surface temperature values for 1982–2017, near-surface wind for 1988–2017. and sea level anomalies for 1993–2017, obtained from satellite data, the seasonal variability of the hydrodynamic characteristics of the upper water layer in the vicinity of the Benguela upwelling is investigated. It is shown that the thermal upwelling index averaged over the entire area with lower temperature values does not give a correct idea on the seasonal course of the water lifting rate in the upwelling zone due to the significant horizontal advection of waters of upwelling origin. The seasonal variations of the vertical velocity of wind origin in the Benguela upwelling zone are characterized by the presence of two extremes from October to March, which is manifested in the predominance of the semiannual harmonic. At the same time, the thermal upwelling index in the zone of distribution of upwelling waters is subject to seasonal variability with an annual period.