Black Sea Ocean Heat Content Anomaly (0-300m) time series and trend from Reanalysis & Multi-Observations Reprocessing

'''DEFINITION'''

Ocean heat content (OHC) is defined here as the deviation from a reference period (1993-2014) and is closely proportional to the average temperature change from z1 = 0 m to z2 = 300 m depth. Further details and the formulation of OHC can be found in the quality information document (QUID) of the corresponding ocean monitoring indicator (OMI). 
Time series of  monthly area-averaged OHC is provided for the Black Sea (40.86°N, 46.8°N; 27.32°E, 41.96°E) and is evaluated in areas where the topography is deeper than 300 m. The Azov and Marmara Seas are not considered.
The quality evaluation of OMI_CLIMATE_OHC_BLKSEA_area_averaged_anomalies is based on the “multi-product” approach as introduced in the second issue of the Ocean State Report (von Schuckmann et al., 2018), and following the MyOcean’s experience (Masina et al., 2017). An ensemble mean and its associated spread were derived using four products: three global and one regional (Black Sea) dataset: 
The Global Ocean- Delayed Mode gridded CORA- In-situ Observations objective analysis in Delayed Mode (INSITU_GLO_PHY_TS_OA_MY_013_052, CORA5.2; Szekely et al., 2019).
The Multi Observation Global Ocean 3D Temperature Salinity Height Geostrophic Current and MLD (MULTIOBS_GLO_PHY_TSUV_3D_MYNRT_015_012, AMOR3D; Guinehut et al., 2012). 
The Global Ocean Physics Reanalysis (GLOBAL_MULTIYEAR_PHY_001_030; Lellouche et al., 2021).
The Black Sea Physics Reanalysis (BLKSEA_MULTIYEAR_PHY_007_004; Lima et al., 2021).

'''CONTEXT'''
Knowing how much and where heat energy is stored and released in the ocean is essential for understanding the contemporary Earth system state, variability and change, as the oceans shape our perspectives for the future.
Several studies discuss warming in the Black Sea using either observations or model results (Akpinar et al., 2017; Stanev et al., 2019; Lima et al., 2020). Using satellite sea surface temperature observations (SST), Degtyarev (2000) detected a positive temperature trend of 0.016 ºC years-1 in the 50-100 m layer from 1985 to 1997. From Argo floats Stanev et al. (2019) found a warming trend in the cold intermediate layer (CIL; at approximately 25 – 70 m) of about 0.05 oC year-1 in recent years. The warming signal was also present in OHC analyses using an earlier version of the Black Sea regional reanalysis which revealed a positive trend of 0.88±0.18 W m-2 in the upper layers (0-200 m). This warming has resulted in the disappearance of the CIL in the Black Sea in recent years, as well as an increased frequency of marine heatwaves in the region (Mohamed et al., 2022).

'''KEY FINDINGS'''
Time series of OHC anomalies present a significant interannual variability, altering between cool and warm events. This important characteristic becomes evident over the years 2012 to 2015: a negative minimum in the OHC anomaly is registered close to – 2.00 x 108 J m-2 in 2012, followed by positive values around 1.50 x 108 J m-2 in 2013 and above 2.0 x 108 J m-2 most of time in 2014 and 2015. Since 2005 the Black Sea has experienced an increase in OHC, and record OHC values were noticed in January 2021. 
The increase in OHC weakens the CIL, whereas its decreasing favours the CIL restoration (Akpinar et al., 2017). The years 2012 and 2017 exhibited a more evident warming interruption that induced a replenishment of the CIL (Lima et al. 2021). Beginning in February 2021, OHC anomalies began to decline again. A very weak CIL formed in March 2022, as reported by Çokacar et al. (2024). 

'''DOI (product):''' 
 https://doi.org/10.48670/moi-00306