Physical and biogeochemical parameters of the Mediterranean Sea during a cruise with RV <i>Maria S. Merian</i> in March 2018

Abstract

Abstract. The last few decades have seen dramatic changes in the hydrography and biogeochemistry of the Mediterranean Sea. The complex bathymetry and highly variable spatial and temporal scales of atmospheric forcing, convective and ventilation processes contribute to generate complex and unsteady circulation patterns and significant variability in biogeochemical systems. Part of the variability of this system can be influenced by anthropogenic contributions. Consequently, it is necessary to document details and to understand trends in place to better relate the observed processes and to possibly predict the consequences of these changes. In this context we report data from an oceanographic cruise in the Mediterranean Sea on the German research vessel Maria S. Merian (MSM72) in March 2018. The main objective of the cruise was to contribute to the understanding of long-term changes and trends in physical and biogeochemical parameters, such as the anthropogenic carbon uptake and to further assess the hydrographical situation after the major climatological shifts in the eastern and western part of the basin, known as the Eastern and Western Mediterranean Transients. During the cruise, multidisciplinary measurements were conducted on a predominantly zonal section throughout the Mediterranean Sea, contributing to the Med-SHIP and GO-SHIP long-term repeat cruise section that is conducted at regular intervals in the Mediterranean Sea to observe changes and impacts on physical and biogeochemical variables. The data can be accessed at https://doi.org/10.1594/PANGAEA.905902 (Hainbucher et al., 2019), https://doi.org/10.1594/PANGAEA.913512 (Hainbucher, 2020a) https://doi.org/10.1594/PANGAEA.913608, (Hainbucher, 2020b) https://doi.org/10.1594/PANGAEA.913505, (Hainbucher, 2020c) https://doi.org/10.1594/PANGAEA.905887 (Tanhua et al., 2019) and https://doi.org/10.25921/z7en-hn85 (Tanhua et al, 2020).

Optical Properties and Biochemical Indices of Marine Particles in the Open Mediterranean Sea: The R/V Maria S. Merian Cruise, March 2018

“…The survey was carried out on board the German R/V Maria S. Merian from March 2nd to April 3rd 2018 (Figure 1). The cruise started at Heraklion, Crete, Greece and ended in Cadiz, Spain (Hainbucher et al, 2020). In total, 136 CTD casts were conducted during the cruise materializing a complete east-to-west Mediterranean transect plus another one in the Ionian Sea.…”

“…strategy can be found in Hainbucher et al (2020). At 62 stations (with depth <3,000 m) the LISST-Deep was deployed along with the rosette system to obtain optical parameters i.e., beam attenuation coefficient, particle volume concentration, particle median diameter, and the slope of PSD.…”

“…The horizontal patterns of δ 15 N-PN observed in the mixed layer of the EMed reflect the interplay of isotopically distinct N sources and the degree of N utilization during primary production. Extremely low δ 15 N-PN values in NO 3 replete waters (Hainbucher et al, 2020) at stations 47 and 9 give evidence for diazotrophic N 2 fixation or atmospheric NO x deposition in the ultra-oligotrophic EMed (Pantoja et al, 2002;Emeis et al, 2010;Moon et al, 2016). Moreover, low values at still relatively high nitrate levels in the Alboran Sea point towards preferential assimilation of 14 N, however, the ambient nitrate most probably had a higher δ 15 N signature due to its Atlantic origin (Pantoja et al, 2002).…”

“…On the other hand, particle concentrations and particle mean sizes remain stable, in defiance of signals from the surface waters such as a sinking algal bloom. At the same time, nitrate concentrations reach their maxima and O 2 concentrations their minima (Hainbucher et al, 2020). Interestingly, all these outliers (even in the Sicily Strait) have been sampled between 500 and 1,500 m within the TMW.…”

“…The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: CTD data: https:// doi.org/10.1594/PANGAEA.905902 (Hainbucher et al, 2020); Laser in situ Scattering and Transmissometry (LISST-Deep) data: https://doi.pangaea.de/10.1594/PANGAEA.934055; Biochemical data of marine PM (POC, PN, δ 13 C-POC, δ 15 N-PN): https://www. ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0218894.html and https://doi.org/10.1594/PANGAEA.905887.…”