Page 110 - Çevre Şehir İklim İngilizce - Sayı 3

The Study of Deoxygenation and Mucilage Formation in The Marmara Sea
Using Novel Oceanographic Approaches in The Frame of Marmod Project

In the expeditions conducted with R/V Bilim-2 in 2021 (June, July and
September), outbreak, spread and elimination of mucilage event was monitored
with marine parameters. During this expedition conducted for understanding
the reasons of mucilage event in 2021, the layers of mucilage were not observed
in September (2021) which were once found trapped especially at the depth of
10-25m, detected intensively through sensor data as well as the grid modeling.
No mucilage formation was found in deep water samples and various surface
and sediment samples at the depth from 20 to 50m. In addition, no mucilage
formation was observed in the modellings for the Çanakkale Strait and outlet
of the Aegean Sea (ODTÜ-DBE, ÇŞİB, 2021: 103).
According to the first analyses, a part of the mucilage, which was previously
observed to be trapped in the surface layer, flowed out from Çanakkale Strait through
westward Black Sea based current that is active in this layer, remaining a part of it in the
interlayer. It underwent degradation here by the aerobic bacteria. In September
(2021) study, there was no findings that mucilage passed under the interlayer
except for coastal (<20-30 m depth) regions (ODTÜ-DBE, ÇŞİB, 2021: 103).
When compared to the oxygen values measured during (June 2021) and
after (September 2021) the mucilage period, it was observed that interlayer
transitional waters (20-100 m) of the Marmara Sea contained lesser dissolved
oxygen than the levels in June. While hypoxia threshold which is 80 µM,
especially, in Eastern Marmara Sea and Gulf of İzmit, also called as Çınarcık
Basin, was at the limit of 28-30m in these regions at the end of June, it
reached to a depth of 22-25 m. This showed that if there is no new water
input containing oxygen, surface waters will come under substantial oxygen
pressure as a result of late summer stratification as well as bacterial dissolution
of organic layer which also includes the mucilage mentioned above. Besides,
very low oxygen levels prevailing in the deeper waters of Marmara (>200m)
remained the same without major changes (ODTÜ-DBE, ÇŞİB, 2021: 103).
The study performed in September revealed an oxygen inflow and new water
input to the interlayer in the range of 30-100m in the southern shelf representing,
in particular, the Gulf of Erdek, around Marmara Island and the frontal Susurluk
River Delta which was not observed in June. With three Scanfish cross-sections
in south-north direction, it was found that this water inflow pumped new oxygen
especially into the southern part, but had no effect on the central and northern
Marmara. It was found that this new oxygen flow into the Southern Marmara
reaches up to Gulf of Gemlik in particular. The effects of mucilage was mitigated
slightly in these regions due to this new Mediterranean water in-flow. In addition,
it was observed that a slight oxygen inflow from Mediterranean water still
continued between 400-700m which is constantly observed in the deep basin,
and it was concluded that Marmara was still kept alive by Mediterranean water
flowing from the Strait of Çanakkale (ODTÜ-DBE, ÇŞİB, 2021: 103).

Year 2 / Issue 3 / January 2023 95