Impact of Winter Cooling on Water Vertical Entrainment and Intensity of Phytoplankton Bloom in the Black Sea

Abstract

Vertical entrainment of nutrients and phytoplankton from the subsurface layers in autumn -winter is a cause of the surface phytoplankton bloom in the Black Sea in winter. Relationship of the winter heat flux and the sea surface temperature (SST) with the integral and surface phytoplankton biomass is assessed based on a series of simulations performed due to a 1D-biogeochemical model. The results show that during severe winters, intensity of phytoplankton bloom is 50% higher than that in warm winters. Winter entrainment of nutrients influences the phytoplankton biomass in the subsurface layer in summer, namely, after cold winters its maximum value exceeds the analogous one after warm winters by ≈30%. In-situ data is used to estimate the relation between the upper mixed layer depth and density, and the integral concentration of nitrates and phosphates in various regions of the basin. It is revealed that growth of the upper mixed layer density from 1014.0 to 1014.2 kg/m 3 results in increase of the integral concentration of nutrients in the upper layer by 2-2.5 times in the center and on the periphery of the basin; and when the density value achieves 1014.5 kg/m 3 the integral concentration becomes higher by 4-5 times. Thus the upper mixed layer density serves a good indicator of intensity of the nutrients inflow to the sea upper layers. Impact of winter cooling upon the upper mixed layer density is investigated using the model and in-situ data. It is shown that density equal to 1014.2 kg/m 3 is achieved in the basin center at SST 7.5-8° C, and on the sea periphery -at 6.5° C. The maximum density value 1014.8 kg/m 3 is recorded in the center of the sea (depth exceeds 2000 m) at SST < 5.5° C. During the same atmospheric conditions, the vertical nutrient transport is different in various regions of the Black Sea, which can affect the spatial features of bloom intensity in the basin. Acknowledgements:The data were obtained and processed within the framework of the State Order No. 0827-2014-0011 "The research of regularities of marine environment condition changes on the basis of operational observations and the data of marine area condition nowcast, forecast and reanalysis system" ("Operative oceanography" code); model calculations were carried out with the financial support of RFBR

Three Typical Hydrological-Hydrochemical Situations Near the Danube River Mouth Based on the Marine Hydrophysical Institute Research Expeditions in 1997-2013

“…The assumptions on the ongoing process of photosynthesis (winter blooming of phytoplankton near the Danube mouth was observed not once by chlorophyll a distribution in the surface waters [4]) are also confirmed by the data on water saturation with oxygen. In the open part of the shelf, water saturation with oxygen constituted 97-98%; at the same time, near the coast it was higher, attaining 100-102% opposite the Sulina branch and 108-110% opposite the Chilia branch ( Fig.…”

“…F i g. 1. Propagation of the Danube transformed freshwater flow in summer based on chlorophyll distribution in the surface waters [2] The freshwater runoff in this region provides phytoplankton with the inorganic forms of nitrogen, phosphorus, and silicon in course of a whole year that stimulates phytoplankton to bloom at the NWS not only in spring and autumn, but also in winter [3,4]. However, the most environmentally dangerous situation on the NWS is observed in the warm season.…”

Seasonal Stages of Chlorophyll‐a Vertical Distribution and Its Relation to the Light Conditions in the Black Sea From Bio‐Argo Measurements

“…MODIS satellite scanner measurements of Chla, together with Bio‐Argo data, show the strong impact of storms on the development of anomalous blooms of phytoplankton in the warm period of a year (Kubryakov, Zatsepin, et al., 2019). Long‐term analysis of satellite and in situ data show that the seasonal surface peak of Chla was controlled by river discharge in the shelf areas and by the start of winter convection in the deep areas of the basin (Finenko et al., 2014; Krivenko & Parkhomenko, 2010; Kubryakova et al., 2018). However, satellite data give us information only about surface variability, and they are unable to elucidate the important features of Chla seasonal dynamics, such as its subsurface maximum.…”

“…In situ investigations show that column‐averaged Chla generally have three seasonal maximums (winter–early spring, summer, and autumn) (Demidov, 1999; Finenko et al., 2005; Krivenko, 2010; Kubryakova et al., 2018; Vedernikov & Demidov, 1993), which is different from surface Chla characterized by two maxima in late autumn and early spring (Berseneva et al., 2004; Demidov, 2008; Krivenko & Parkhomenko, 2010). The general feature of Chla vertical distribution is deepening of the peak during a warm period of a year and a formation of a so‐called deep chlorophyll maximum (DCM) (Sorokin, 1983; Vedernikov & Demidov, 1993), similarly as in the other areas of the World Ocean (Cullen, 2015).…”

The Black Sea Mixed Layer Depth Variability and Its Relation to the Basin Dynamics and Atmospheric Forcing

“…The reason for this is the impact of basin dynamics in severe winters, the northeastern wind intensifies, which is associated with an increase in the cyclonic vorticity of the wind over the basin [14,20,21]. This causes an intensification of the cyclonic circulation and upraise of the main pycnocline (pycno-halocline) in the sea center, which limits the vertical mixing [14,22].…”