Climate-Driven Changes in the Black Sea in Front of the Bulgarian Coast

Bulgarian Journal of Agricultural Science, 19 (Supplement 1) 2013, 21–29 Agricultural Academy

CLIMATE-DRIVEN CHANGES IN THE BLACK SEA IN FRONT OF THE BULGARIAN COAST

S. DINEVA Institute of Fish Resources, BG – 9000 Varna, Bulgaria

Abstract

DINEVA, S., 2013. Climate-Driven Changes in the Black Sea in front of the Bulgarian Coast. Bulg. J. Agric. Sci., Supplement 1: 20–29

The world is heating up and assessment of the magnitude of temperature increases refers to the Earth’s seas and oceans. The seas and oceans act as a giant rechargeable battery for the Earth. It takes a lot of energy and time to change sea temperature so that seas and oceans can be called the ‘memory’ of the Earth’s climate system. The Black Sea in front of the Bulgarian coast becomes climate change affected area. Research in the 30-mile Black Sea zone in front of the Bulgarian coast, down to 100-m isobaths was done, with aim climate-driven changes to be established. In-situ measurements of temperature, salinity, oxygen and oxygen saturation were done. Processing of samples for nutrients was performed via uniﬁ ed methods for marine waters. Climate-driven transformation of the thermo-haline structure was ascertained. Because of warming, the Black Sea Cold Intermediate Layer in front of the Bulgarian coast was warmer in the frame of isotherms of 8˚C, with greatly elevated bottom border. Salinity was above the long-term average throughout the 100 m investigated layer. The greatly elevated Cold Intermediate Layer bottom border brought about rise of high-salinity deep waters. Owing to crucially reduced fresh water inputs, extremely low were the concentrations of nutrients. The organic nitrogen share was dominating at total nitrogen formation in the open-sea.

Key words: Black Sea, climate change impact, Danube River stream Abbreviations: Cold Intermediate Layer (CIL); Cold Intermediate Water (CIW); Organic nitrogen (ON); Sea surface salinity (SSS); Sea surface temperature (SST); Total inorganic nitrogen (TIN); Total nitrogen (TN)

Introduction climate system. Tracking sea surface temperature over a long period is the most reliable way of measuring the The world is heating up and the assessment of the precise rate at which global temperatures are increasing. magnitude of temperature increases refers to the Earth’s Heat energy slowly released from the sea is the domi- seas and oceans. The seas and oceans function as vast nant driver of atmospheric circulations and weather pat- reservoirs of heat. Covering the greater part of the tern. Sea surface temperature inﬂ uences the rate of en- Earth’s surface, the oceans directly absorb the majority ergy transfer to the atmosphere, as evaporation increases of solar heat, storing it for long periods by comparison to with temperature. either the land or atmosphere. The seas and oceans act as The predicted effects of climate change are numer- a giant rechargeable battery for the Earth. It takes a lot of ous (Dineva, 2010; Dineva and McKay, 2012) and some energy and time to change sea temperature so that seas effects of recent climate change may already be occur- and oceans can be called the ‘memory’ of the Earth’s ring. There is much need to assessing the rate, magnitude

E-mail: [email protected] 22 S. Dineva and duration of unwelcome global and regional climate- driven events related to water environment. Varna Black Sea low-salinity surface waters by river origin overlie high-salinity deep waters by Mediterranean origin, and as a result, a permanent pycnocline (halocline) develops, with a depth between 100–150 m varying horizontally according to the local hydrodynamics, that inhibits the exchange between the surface and deep waters. Owing to these conditions, the Black Sea is almost anoxic, with oxygen only in the upper 150m layer (13% B-5 of the sea’s volume), and hydrogen sulphide and meth- ane in the deep waters. The atmospheric forces affect only the sub-surface layer and cold intermediate waters (Grégoire and Beckers, 2004). The most important characteristics of the Black Sea The Black Sea vertical stratifi cation (Ryabinin et al., 1991; Grégoire A and Beckers, 2004) are the sharp halocline (from greek: hals – salt) from the sea surface down to 200 m (upper halocline from 0 m down to 20 m, and permanent halo- Cape Kaliakra cline – from 50 m down to 200 m), and the Cold Inter- mediate Layer. The western periphery of the Black Sea is unlike eastern mainly owing to penetration of Danube Transformed Waters (Sapozhnikov, 1992) and waters by Cape Galata river origin of northwestern part of the sea. The Black Sea in front of the Bulgarian coast (Di- neva, 2008; Dineva, 2009; Dineva, 2010) becomes high Cape Emine sensitive to climate change and climate footprint assessment is much needed. Notable temperature extremes during 2003 included a severe heat wave (NOAA, 2004) in the summer of 2003 across Europe. Research in the 30-mile Black Sea zone in front of the Bulgarian coast, down to 100-m isobaths was done in 2003, with aim climate-driven changes to be established. B

Fig. 1. Maps of sampling stations: Material and Methods (A) Varna Bay – Control St. B5. (B) The zone in front of the Bulgarian Black Sea coast along The 30-mile Black Sea zone in front of the Bulgar- Capes Kaliakra, Galata and Emine ian coast was studied down to 100-m isobath (Dineva, 2004) in 2003. Observations were performed aboard the is a high quality, high accuracy multiparameter probe for IFR R/V Prof. A. Valkanov. Research was done along oceanographic measurements of physical and chemical Capes Kaliakra, Galata and Emine, with sampling at 1, parameters, with calculations according to UNESCO 3, 10, 20 and 30 miles, and at St. B5 in the Varna Bay formulas. Comprehensively study of the essential forms (Figure 1). of nitrogen, including total inorganic nitrogen and total Measurements of temperature, salinity, oxygen and nitrogen in the 30-mile zone in front of the Bulgarian oxygen saturation were done by CTD 60 (2001), which Black Sea coast (Dineva, 2004) was carry out as part Climate-Driven Changes in the Black Sea in front of the Bulgarian Coast 23 of Danubs project. Samples were collected at standard A depths (0, 10, 25, 50, 75, and 100 m) to study NO2-N,

NO3-N, NH4-N, total inorganic nitrogen, organic nitrogen, and total nitrogen. Processing of samples was performed via uniﬁ ed methods for marine waters (Gashi- na, 1993; UNESKO, 1994). Concentrations of NO2-N,

NO3-N and NH4-N were established (Dineva, 2004) by Japanese Spectrophotometer HITACHI-U 2001 UV/Vis (1995). Regional Environmental Inspections – Varna found Keldal’s nitrogen concentrations with a Gerhardt system for mineralization and distillation.

Results and Discussion

After 2002, global temperatures remain high. In 2003 (NOAA, 2004), global temperatures (IPCC, 2001) were B above the long-term average, ranking 2003 the second warmest year on record, which tied 2002. Temperatures for the year were above long-term average across large parts of Asia, Europe and the western United States. Warmer-than-average temperatures also covered much of South America, Australia, Canada and parts of Africa. Over 2003, notable temperature extremes comprised severe heat wave in the summer of 2003 across Europe (NOAA, 2004). Daily maximum temperatures ranged from 30 to 37°C across France, Switzerland and the Mediterranean region, killing approximately 25.000 people. The record summer heat wave contributed to the Fig. 2. Black Sea summer temperatures in the 30-mile large annual anomalies in Europe. The all-time maxi- zone in front of the Cape Galata (coastal and open sea waters) in 2003, with respect to the 1992–2000 mean: (A) mum temperature record in the United Kingdom was Summer sea temperatures (˚C) in the 100 m layer. (B) broken on August 10, when the mercury reached 38.1°C Summer temperature positive anomalies (˚C) in the 100 at Kent. m layer Sea surface temperature in front of the Bulgarian coast in August 2003 was 0.86°C above the 1992-2000 isotherms of 8˚C (Vladimirtsev, 1964), and covers the mean (Dineva, 2007), and sea temperature was with criterion about limits of salinity: 18.6 psu < S < 20.0 anomaly in excess of 1.26°C at 10 m depth. The adjacent psu (Ryabinin et al., 1991). The CIL thickness depends Figure 2 depicts warmer than average sea temperatures on the severity of previous winter as increase of storms that were spread in front of Cape Galata. Sea tempera- brings about deeper penetration of winter cooling. The tures in this region were 1.41°C above the 1992-2000 CIL is presented throughout the whole year, although average in the 10-25 m layer (Figure 2B.). during much of the year it is enough near to well warm In the Black Sea а Cold Intermediate Layer com- waters (Bogdanova, 1959a). According to Ovchinnikov mences near on 40 m depth and infl uences on the tem- and Popov (1987), CIL is forming in the centres of the perature distribution, been in the summer a physical cyclonic gyres in the central part of the sea during term border between sub-surface and deep waters (Ovchin- of maximum cooling of the surface, and the Basic Black nikov, 1989). Vertically, the CIL is situated between Sea Current spreads these waters. The winter convection 24 S. Dineva in the cyclonic gyres is the basic source of replenish- and +0.39˚C. Because of warming, the Black Sea Cold ment and refreshing. Later on, a new analysis of the Cold Intermediate Layer in front of the Bulgarian coast was Intermediate Water formation was presented by Ivanov, warmer in the frame of isotherms of 8˚C, with greatly Beşiktepe and Özsoy (1997), based on the new data sets, elevated bottom border than 90s – with 46 m in front of having high resolution and full basin coverage. They es- Cape Galata and with 35 m in front of Cape Emine. The tablished that CIL forming process is an outcome of both upper border was raised only with 4 m in front of Cape convective and advective contributions, most actively Galata, and with 10 m in front of Cape Emine. Based taking place along the ‘convergence zone’. on 1992–2000 mean (Dineva, 2007), the CIL vertical In August 2003, the upper CIL border was on 45 range was reduced with 42 m in front of Cape Galata, m depth at 20 miles in front of Cape Galata, on 42 m and with 25 m in front of Cape Emine, i.e. CIW volume depth at 30 miles in front of Cape Galata, and on 38 m was greatly reduced than 90s. depth at 20 miles in front of Cape Emine. The bottom A temperature anomaly of waters on 25 m depth in CIL border was on 89 m depth at 30 miles in front of front of Cape Emine, which are situated above the CIL, Cape Galata, and on 97 m depth at 20 miles in front of based on 1992–2000 mean (Dineva, 2007) was –4.66˚C. Cape Emine. Temperature anomalies of CIW, based on It was due to reduced intensity of the turbulence ex- 1992–2000 mean (Dineva, 2007) were between +0.04˚C change in the layer of sharper thermocline, which has inhibited the heat penetration into that layer. A Salinity of the 30-mile zone in front of the Bulgarian Black Sea coast during 2003 was above the long-term (1992–2000) average (Dineva, 2007) throughout the 100 m investigated layer (Figures 3 and 4). Salinity of the Bulgarian Black Sea was unusually high in April under impacts of several factors: slight Danube River infl uence, upwelling, and slight coastal river run-off. Sea surface salinity was 16.93 psu at 10 miles in front of Cape Galata and was increased in the direction of the coast: at 3 miles it was 17.00 psu, and at 1mile – 17.39 psu. Salinity was highest and abnormal in B the Varna Bay, with SSS – 17.98 psu, and in the bottom layer – 18.13 psu. A sharp SSS decrease has occurred in May. The stream of Danube transformed waters was at 10 miles in front of Cape Galata (Figure 5). The infl uence was throughout the whole layer, but most affected was the 10 m layer, with SSS – 15.08 psu, and on 10 m depth salinity was 15.80 psu. In the Varna Bay, only surface waters were refreshed, and SSS minimum of 15.45 psu was recorded. Salinity was again high in August (Figure 3), above the long-term (1992–2000) average throughout 100 m layer, with a positive SSS anomaly of 1.05 Fig. 3. Black Sea monthly salinity variability at 3 miles in front of Cape Galata (Bulgarian Control psu, and greatest positive anomaly of 1.63 psu at 100 m Station in the coastal zone) in 2003 with respect depth (Figure 4). to the long-term (1995–2000) average: The dissolved oxygen is an indicator of the balance (A) Sea surface salinity (psu). of the marine ecosystem, which gives a possibility for (B) Sea bottom salinity (psu) assessment of the production-destruction processes (Di- Climate-Driven Changes in the Black Sea in front of the Bulgarian Coast 25 neva, 2005; Dineva, 2007). There are three main sources quantities of nutrients enter coastal waters. These nutri- of oxygen in the sea – direct diffusion from the atmo- ents stimulate the rapid growth of phytoplankton. When sphere, wind and wave action, and photosynthesis. From the produced organic matter settles into the deeper bay these, photosynthesis by aquatic plants and phytoplank- waters, its decomposition can deplete the dissolved oxy- ton is very important (Sapozhnikov, 1992). Oxygen de- gen, and the result is death of fi shes. pletion occurs when oxygen consumption exceeds oxy- In March, the nearest coastal zone in front of Cape gen production. Increases in oxygen consumption can be Galata was most oxygen super-saturated – 126.49% in the caused by an over-abundance of marine plants or algae layer of 1 mile offshore. In May, the highest super-satura- in the ecosystem, increased organic waste entering the tion was again at 1 mile in front of Cape Galata – 121.08 water, death and decay of organic matter, or by certain % (5 m), while much different was the state of the Varna chemicals that remove oxygen directly from the water Bay – an increased oxygen defi ciency (82–88% satura- column. Oxygen plays a very active role in the chemistry tion), recorded as early as April (90–94% saturation). In and biology of coastal waters, and its concentration is August, the waters in front of the Bulgarian coast were a major indicator of water quality. In some areas, large oxygen super-saturated down to 75–80 m, with oxygen A C

0 m 2,0 10 m Salinity 25 m 1,5 Anomalies Depth (m) (PSU) 50 m 1,0 Based on 75 m 1992 - 2000 0,5 Mean 100 m 0,0

Fig. 4. Black Sea summer salinity in the 30-mile zone in front of the Bulgarian coast (coastal and open sea waters) in 2003 with respect to the average salinity from 1992 to 2000: (A) Summer sea salinity (psu) in the 100 m layer in front of Cape Galata. (B) Positive anomaly of the summer salinity (psu) in the 100 m layer in front of Cape Galata. (C) Summer sea salinity (psu) in the 100 m layer in front of Cape Emine. (D) Positive anomaly of the summer salinity (psu) in the 100 m layer in front of Cape Emine 26 S. Dineva

(Bogdanova, 1959b), and this maximum is as bigger as the thermocline is sharper. The peaks are not so much owing to the intensity of photosynthesis but rather owing to favourable conditions for oxygen accumulation, according to diminution of the vertical exchange in the layer of maximum gradient of density. The forming of sustainable layer in the zone of photosynthesis creates conditions for accumulation of the produced oxygen in this layer. Owing to the process denitriﬁ cation, the amount of Fig. 5. May Sea surface salinity (psu) in the Varna Bay available N (nitrate, nitrite and ammonium) appears to (B5), and in the Bulgarian Black Sea coastal zone in front of Cape Galata – at 1 mile offshore (G1), 3 miles be the limiting nutrient in the sea (Topping, 1976), un- offshore (G3), and 10 miles offshore (G10) like fresh water systems where phosphate appears to be the nutrient controlling the production of plant life. The A denitriﬁ cation process results in the formation of nitrite

and ﬁ nally ammonia, and in some extreme cases, N2 gas is produced and there is a net loss from the system (Horn, 1972; Leonov, 1980). Global precipitation was below the 1961–1990 average in 2003 for third year in a row (NOAA, 2004), and has negatively affected the Black Sea in front of the Bulgarian coast and its watershed. The adjacent Figure 6 depicts this negative impact on the nutrients. Nitrite and nitrate nitrogen concentrations were sig- B niﬁ cantly below the long-term average (Dineva, 2007) in March, and the situation has continued to deteriorate through the year. In May, nitrate nitrogen concentration was highest at 10 miles in front of Cape Galata – in the stream of Danube transformed waters (5–10 m layer). In August, in the 50 m open-sea layer in front of Cape Galata and Cape Emine there were only traces of nitrite nitrogen and below 50 m there was no nitrite. The nitrate concentration was considerably lowered – 0.29 μM throughout surface-bottom layer. The situation was similar along Kaliakra transect – minimal nitrite and nitrate nitrogen concentrations, including a considerable num- Fig. 6. Monthly nitrate nitrogen (μM) variability ber of nitrite nitrogen concentrations under the detection at 3 miles in front of Cape Galata (Bulgarian Control limit. The nutrient fund was in a crucial state owing to Station) in 2003 with respect to the long-term (1995–2000) average: (A) In the surface waters. severe drought, minimal river run-off, and increased (B) In the bottom waters consumption by phytoplankton. In 2003, ammonium nitrogen depletion was reached only in the bottom waters saturation maximum of 181.10% at 10 miles in front of at 1 mile in front of Cape Galata in the summer. The Cape Kaliakra, 29 m depth. Along all transects, the peaks maximal year’s ammonium concentration was recorded of oxygen super-saturation down on the vertical were in in April in the surface waters of 1 mile in front of Cape accordance with the rule that the maximum of the dis- Galata – 10.51 μM. A high ammonium nitrogen concen- solved oxygen occurs in the layer of the thermocline tration – 9.81 μM was established in the Varna Bay sur- Climate-Driven Changes in the Black Sea in front of the Bulgarian Coast 27

A C

B D

Fig. 7. Ratio between nitrite nitrogen, nitrate nitrogen and ammonium in the layers of Varna Bay (B5), and at 1 mile in front of the Bulgarian Black Sea coast (Coastal zone) in August 2003: (A) in front of Cape Kaliakra (K1); (B) in front of Cape Galata (G1); (C) in front of Cape Emine (E1); (D) in the Varna Bay (B5)

A C

B D

Fig. 8. Ratio between total inorganic nitrogen (TIN) and organic nitrogen (ON) in the layers of Varna Bay (B5), and at 3 miles in front of the Bulgarian Black Sea coast (Coastal zone) in August 2003: (A) in front of Cape Kaliakra (K3); (B) in front of Cape Galata (G3); (C) in front of Cape Emine (E3); (D) in the Varna Bay (B5) 28 S. Dineva face waters in March. In the Varna Bay under infl uence tained. The elevated greatly CIL bottom border than 90s, of Varna Lake, higher total inorganic nitrogen level than with 46 m in front of Cape Galata and with 35 m in front the coastal zone was formed. TIN concentrations were of Cape Emine, brought about rise of high-salinity deep from crucially low – 0.30 μM (August, 1 mile in front of waters. The waters in front of the Bulgarian Black Sea Cape Galata, bottom) to 17.27 μM (March, Varna Bay, coast were oxygen super-saturated down to 75–80 m in surface waters). In August, TIN distribution at 1 mile in August, approaching 181.10% saturation at 10 miles front of the Bulgarian Black Sea coast and in the Varna in front of Cape Kaliakra, 29 m depth. Nitrite and ni- Bay was as follows on Figure 7. trate nitrogen concentrations were signifi cantly below The summer of 2003 was crucial for the ecosystem. the long-term average throughout the year. In August, The organic nitrogen share was dominant at total nitro- in the 50 m open-sea layer in front of Cape Galata and gen formation (Figure 8). In 2003, TN concentrations Cape Emine there were only traces of nitrite nitrogen, have ranged from 0.30 μM at absence of organic nitro- and below 50 m there was no nitrite. The nitrate concen- gen (summer, 1 mile in front of Cape Galata, bottom) to tration was considerably lowered – 0.29 μM throughout 40.33 μM (summer, 1 mile in front of Cape Kaliakra, surface-bottom layer. The situation was similar along surface). Kaliakra transect – minimal nitrite and nitrate nitrogen concentrations, including a considerable number of ni- Conclusions trite nitrogen concentrations under the detection limit. The nutrient fund was in crucial state owing to severe During severe heat wave across Europe in the summer drought, minimal river run-off, and increased consump- of 2003, SST in front of the Bulgarian Black Sea coast tion by phytoplankton. Total inorganic nitrogen concen- in August was 0.86°C above the 1992–2000 mean, and trations were from extremely low – 0.30 μM to 17.27 sea temperature was with anomaly in excess of 1.26°C μM. The organic nitrogen share was dominant at total at 10 m depth. In front of the Cape Galata, temperature nitrogen formation. Over the year, total nitrogen con- was 1.41°C above the 1992–2000 average in the 10-25 centrations were from 0.30 μM (at absence of organic m layer. Down, the CIL was also affected. Temperature nitrogen) to 40.33 μM. anomalies of Cold Intermediate Water based on 1992- 2000 mean were between +0.04˚C and +0.39˚C in front Acknowledgements of the Bulgarian coast. Because of warming, the Black The results presented stem from the project „Nutrient Sea CIL was warmer in the frame of isotherms of 8˚C, Management in the Danube Basin and its Impact on the with greatly elevated bottom border than 90s. Based on Black Sea“ (daNubs) supported under contract EVK1- 1992-2000 mean, the CIL vertical range was reduced CT-2000-00051 by the Energy, Environment and Sus- with 42 m in front of Cape Galata and with 25 m in front tainable Development (EESD) Programme of the 5th EU of Cape Emine, i.e. CIW volume was greatly reduced Framework Programme. than 90s. During 2003, climate-driven transformation of the haline structure was established in the 30-mile References investigated zone in front of the Bulgarian Black Sea coast. Salinity was above the long-term (1992–2000) Bogdanova, А., 1959a. Upwelling/Downwelling and thermal average throughout the 100 m surveyed layer. Owing to regime of the Black Sea. Works of the Sevastopol Biologi- upwelling and slight river run-off, salinity of the Bulgar- cal Station, 11: 262–283 (Ru). ian Black Sea was unusually high in April. Salinity was Bogdanova, A., 1959b. Upon the question of vertical distribution of the oxygen in the Black Sea. Works of the Sevasto- again high in August, above the long-term (1992–2000) pol Biological Station, 11: 297–316 (Ru). average throughout 100 m investigated layer, with a Dineva, S., 2004. Chapter I. Hydrology and Hydrochem- positive SSS anomaly of 1.05 psu, and greatest positive istry, 2003 Annual Report. In: Bulgarian Report on fi eld anomaly of 1.63 psu at 100 m depth. Strong upwelling and laboratory work in 2003, Nutrient Management in the in the 3-mile zone in front of Cape Kaliakra was ascer- Danube Basin and its Impact on the Black Sea (daNubs Climate-Driven Changes in the Black Sea in front of the Bulgarian Coast 29

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