Impact of the 2014 Major Baltic Inflow on benthic fluxes of ferrous iron and phosphate below the permanent halocline in the southern Baltic Sea

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Temperature (T), salinity (S), dissolved oxygen (DO) concentration, oxygen saturation (DOsat), oxidation reduction potential (Eh), pH and the concentrations of sulfate (SO42–), hydrogen sulfide (H2S), phosphate (PO43–) and ferrous iron (Fe(II)) in water above the sediment measured in the Gdansk Deep during the summer and winter voyages (T, S and DO was measured 1 m and other parameters several cm above the sediment surface)

Voyage	Site	T (°C)	S	DO (cm3 dm–3)	DOsat (%)	Eh (mV)	pH	SO42– (mmol dm–3)	H2S (μmol dm–3)	PO43– (μmol dm–3)	Fe(II) (μmol dm–3)
VIII 2015	P1	7.27	13.37	0.86	11	162	7.81	16.19	1.10	12.56	0.13
	P1A	7.32	13.21	1.43	18	224	7.80	14.90	0.00	8.21	0.18
	P1B	7.22	13.39	1.51	19	247	7.78	15.59	0.00	12.66	0.23
II 2016	P1	6.32	12.31	0.58	7	92	7.90	4.99	27.22	27.27	0.42
	P1A	6.63	11.44	1.17	15	194	7.90	11.04	17.80	24.66	0.51
	P1B	6.35	11.45	1.37	17	217	7.88	10.63	20.85	25.68	0.53

Benthic fluxes of phosphate (FPO43–) and iron (FFe(II)) in different regions of the Baltic Sea

Region	Estimation method	FPO43– (μmol m–2 hr–1)	References
Gullmarsfjorden	Porewater gradient calculations	5.42	Sundby et al. 1986
Gulf of Finland		0.002–0.07	Ignatieva 1999
Gulf of Gdansk		–0.1–7.9	Graca 2009
Gdansk Deep		5.3–5.7	Graca et al. 2006
		2.12–2.56	Łukawska-Matuszewska & Burska 2011
Puck Bay		0.04–3.17	Bolatek 1992
Gotland Basin	Chamber incubations	–0.13–15.67	Viktorsson et al. 2013
		8.33–9.58	Noffke et al. 2015
Region	Estimation method	FFe(II) (μmol m–2 hr–1)	References
Gullmarsfjorden	Porewater gradient calculations	0.83	Sundby et al. 1986
Gulf of Finland	Sediment core incubation	3.93	Lehtoranta & Heiskanen 2003
Gulf of Finland	Chamber incubations	5.84 fluxes of dissolved total iron	Almorth et al. 2009
		0.21 fluxes of dissolved total iron	Pakhomova et al. 2007
Vistula Lagoon		4.16 fluxes of dissolved total iron	Pakhomova et al. 2007

Benthic fluxes of phosphate (FPO43–) and ferrous iron (FFe(II)) and parameters used for calculations

Voyage	Site	Porosity	Diffusion coefficient in sediment (10–6 cm2 s–1)		Concentration gradient in surface sediment (δC δz–1) (μmol dm–3cm–1)		Benthic flux (μmol m–2 hr–1)
			PO43–	Fe(II)	PO43–	Fe(II)	FPO43–	FFe(II)
			VIII 2015	PI	0.975	5.034	4.932	9.468	0.018	1.67	0.31 × 10–2
P1A	0.975	4.145		4.060	18.57	0.046	2.70	0.62 × 10–2
P1B	0.975	5.040		4.937	8.618	0.029	1.53	0.50 × 10–2
II 2016	P1	0.983	4.321	4.233	10.645	0.021	1.63	0.31 × 10–2
	P1A	0.983	4.322	4.234	16.888	0.078	2.58	1.17 × 10–2
	P1B	0.983	4.323	4.233	16.580	0.084	2.54	1.25 × 10–2