Influences of Extreme Upwelling on a Coastal Retention Zone

Coastal retention zones occur in the lee of headlands and within bays of coastal upwelling environments. Because retention zones can concentrate and retain communities of coastal planktonic organisms that would otherwise be advected offshore by wind-driven transport, they are ecologically significant. While the consequences of these zones for plankton retention and recruitment have been examined, the degree to which they remain retentive under variable upwelling intensity is less well understood. This aspect of coastal plankton ecology was studied during 2012 in the retentive upwelling shadow of northern Monterey Bay, California. Environmental and biological data show that exceptionally strong upwelling can greatly diminish resident plankton populations in the upwelling shadow. Results indicate that wind-driven circulation, essential to primary productivity and the formation of retention zones, can surpass levels that allow accumulation and retention of plankton communities.

How do different wind forcing products impact the zonal current variability in the tropical Atlantic?

<p>The upper wind-driven circulation in the tropical Atlantic plays a key role in the basin wide distribution of water mass properties and affects the transport of heat, freshwater, and biogeochemical components like oxygen or nutrients. It is an important component of the Atlantic climate system and the marine ecosystems. Hence, it is crucial to improve our understanding of its long-term variability which largely relies on model simulations due to sparse observational data coverage in earlier periods. In this study the impact of two different wind forcing products on the tropical Atlantic zonal current field is studied in a high-resolution ocean general circulation model. The first forcing product is the Coordinated Ocean-Ice Reference Experiments (CORE) v2 dataset covering the period 1948 to 2009 (Griffies et al., 2009). It has a horizontal resolution of 2°x2° and temporal resolution of 6-hours. The second forcing product is the new JRA55-do surface dataset (Tsujino et al., 2018). This dataset stands out due to its high horizontal (~55 km) and temporal resolution (3 h) which now covers the entire observational period (1958 to present).</p><p>While CORE simulations had difficulties to realistically simulate off-equatorial zonal currents in the tropical Atlantic, in model simulations forced with JRA55-do preliminary results show a clearly improved structure of the equatorial current system. In this study, the used CORE simulation tends to overestimate the strength and vertical extend of the zonal currents especially north of the equator compared to the here used JRA55-do simulation and observations. This might be due to the low resolution of the CORE forcing which cannot resolve smaller scale wind stress and wind stress curl structures.</p><p>Furthermore, the CORE wind forcing exhibit suspicious multidecadal wind variability (He et al., 2016) which presumable impacts the multidecadal variability of the simulated wind-driven circulation in the tropical Atlantic. Here, largest differences of zonal wind stress anomalies (up to ~0.03 N m<sup>-2</sup>) between both forcing products occur north of the equator between 30°-10°W before 1990. CORE shows stronger eastward wind stress anomalies between 1958 and 1970 and stronger westward wind stress anomalies between 1970 and 1990. How this impacts the variability of the equatorial current system is investigated in this study.</p>

The Hydraulic Driving Mechanisms of Cyanobacteria Accumulation and the Effects of Flow Pattern on Ecological Restoration in Lake Dianchi Caohai

Due to rapid increases in socioeconomic development and the human population over the past few decades, the shallow lakes in China have suffered from eutrophication and poor water quality. The conditions in Lake Dianchi Caohai, which is in the northern part of Lake Dianchi, are considered the most serious. The ecological restoration of Lake Dianchi Caohai began in the late 1980s. Lake managers and the public have been puzzled by the lack of a significant response of the water quality to the flow pattern despite the tremendous investment in water quality improvements. Therefore, lake managers desperately need to understand the responses of pollutant behaviors to proposed management measures. In this paper, a depth-averaged two-dimensional hydrodynamic and water quality model based on hydrological data, measured lake bed elevation, and water quality data is developed to simulate the flow field and water quality of Lake Dianchi Caohai. This model was validated using water quality data from the Caohaizhongxin site in 2016, and a close agreement was found between the model results and observations. Wind-driven circulation in Lake Dianchi Caohai was observed in the model results, which revealed that the lake flow pattern was dominated by wind-driven circulation, while the inflow/outflow played only a subsidiary role during this period. The formation of the wind-driven current in Lake Dianchi Caohai could be roughly divided into three stages. The hydrodynamic processes connected with the distribution of chlorophyll a are evaluated and discussed to adequately understand the hydraulic mechanisms driving the accumulation of cyanobacteria. Moreover, we designed three scenarios after comparing all possible operation scenarios to analyze the contributions of each different operation scenario to the water quality improvements. The optimal ecological operation scenario which has the best impacts on the water quality, especially the reduction in Chla and NH3-N concentration, is proposed based on our comprehensive analysis. The water quality improvement and management suggestions proposed in this paper are based on lake flow patterns and make up for previous studies that did not consider the effects of hydraulic characteristics on water quality improvement in Lake Dianchi Caohai.