Effects of sea-ice light attenuation and CDOM absorption in the water below the Eurasian sector of central Arctic Ocean (>88°N)

Figures & data

Fig. 1  Central Arctic Ocean with stations named from Julian days. The yellow line demarcates the water masses of Pacific origin above the line and of Atlantic origin below.

Fig. 2  Station 227 on 14 August with frozen melt ponds and the top of the ice core with a clear layer of deteriorated ice from station 246.

Fig. 3  Temperature (°C), bulk salinity, density (kg m⁻³), brine and air volume (%) at station 226 representing (a–d) multi-year ice and (e–h) station 237 representing first-year ice.

Table 1 Station identification number (Julian day), position, K _d(photosynthetically active radiation [PAR])_i (m⁻¹) of the ice, K _d(PAR)_w (m⁻¹) of the water, transmittance (%), PAR (µmol photons m⁻² s⁻¹) under-ice, chl-a (mg chl-a m⁻³) in the water, chl-a (mg chl-a m⁻²) in the ice, coloured dissolved organic matter (CDOM) absorption coefficient a ₃₇₅ (m⁻¹) in the water, freeboard of the ice (cm), thickness of deteriorated ice (cm) and ice thickness (cm). M signifies multi-year ice and F signifies first-year ice.

ID	Latitude	Longitude	K d—ice (m^−1)	K d—water (m^−1)	Trans. (%)	PAR under ice (µM m^−2 s^−1)	Chl-a water (µg chl-a l^−1)	Chl-a ice (mg chl-a m^−2)	a 375 (m^−1)	Free-board (cm)	Deteriorated ice (cm)	Ice thickness (cm)
226	87 11.70°N	53 35.52°W	1.44	0.25	10.2	17.6	0.19	0.01	0.649	10	7	158 M
227	88 20.80°N	30 45.96°W	1.51	0.15	7.5	16.9	0.06	0.04	0.452	14	8	171 F
228	88 11.83°N	49 35.09°W	1.37	0.31	10.2	18.1	0.08	0.02	0.603	15	6	166 F
229	88 20.85°N	69 36.42°W	1.27	0.22	12.2	11.2	0.13	0.01	0.639	–	6	167 F
231	89 15.36°N	56 16.46°W	1.30	0.19	13.8	11.3	0.12	0.01	0.687	8	8	153 M
232	89 11.39°N	70 50.09°W	1.72	0.17	8.2	10.2	0.11	0.02	1.027	11	10	145 M
233	89 16.79°N	65 27.15°W	1.36	0.18	2.4	1.64	0.16	0.01	0.913	15	8	272 F
234	89 56.11°N	73 41.69°W	1.36	0.25	12.2	8.5	0.12	0.02	0.711	15	7	154 M
235	89 37.19°N	62 16.44°W	1.43	0.18	11.5	12.3	0.18	0.02	0.859	9	8	151 M
236	89 50.23°N	135 55.34°E	1.69	0.19	12.4	14.0	0.13	0.01	0.565	8	8	123 M
237	88 30.06°N	135 34.56°E	1.57	0.18	7.8	8.4	0.17	0.01	0.828	16	10	163 F
238	87 58.55°N	122 09.07°E	1.19	0.09	12.7	8.5	0.10	0.01	0.594	9	10	174 F
239	88 13.15°N	109 25.26°E	1.59	0.09	9.3	5.7	0.15	0.01	0.540	10	14	149 M
241	87 56.55°N	73 29.39°E	1.09	0.19	13.8	5.2	0.05	0.01	0.340	10	15	182 M
242	88 15.64°N	72 51.76°E	1.36	0.07	10.4	9.6	0.10	–	0.343	12	20	166 M
243	89 27.29°N	68 26.98°E	1.76	0.13	10.9	7.6	0.22	0.01	0.352	5	11	126 M
244	88 42.75°N	55 56.35°E	1.58	0.07	8.4	6.1	0.25	0.05	0.387	–	8	156 M
246	88 28.19°N	22 18.17°E	1.68	0.22	6.7	8.0	0.50	0.37	0.413	15	10	161 M
247	88 24.37°N	23 50.83°E	1.53	0.08	8.9	8.0	0.30	0.60	0.477	19	7	158 –
248	87 44.35°N	30 05.51°E	2.01	0.09	5.1	3.0	0.32	0.29	0.406	10	8	148 –
249	87 35.96°N	20 37.56°E	1.75	0.31	1.8	1.2	0.21	0.52	0.415	15	10	230 M
251	85 25.63°N	05 15.95°E	1.57	0.17	8.4	6.5	0.24	0.11	0.303	10	7	157 M
252	84 07.26°N	09 11.02°E	1.64	0.14	10.4	2.7	0.10	0.04	0.238	11	8	130 F
253	83 49.45°N	15 08.02°E	–	0.09	–	4.6	3.50	0.06	0.040	11	–	107 F
255	82 11.69°N	08 41.81°E	–	0.29	–	2.3	1.02	0.08	0.178	14	–	145 M

Fig. 4  (a) Ice thickness (cm), (b) photosynthetically active radiation (PAR) transmittance (τ,%), (c) diffuse attenuation coefficient K _d(PAR) (m⁻¹) of the ice, (d) chl-a (mg chl-a m⁻³) in water below ice, (e) coloured dissolved organic matter (CDOM) absorption coefficient—a ₃₇₅ (m⁻¹) in water, and (f) diffuse attenuation coefficient K _d(PAR) (m⁻¹) in the water.

Fig. 5  Ice thickness (cm) versus ln (photosynthetically active radiation [PAR] transmittance).

Fig. 6  Under-ice light partitioning for the central Arctic Ocean (>88°N). Coloured dissolved organic matter is abbreviated to CDOM.

Fig. 7  Spectral attenuation coefficient K _d(λ) (m⁻¹) at stations 231 and 246 and in pure water (Pope & Fry 1997).

Fig. 8  Spectra of absorption coefficients (m⁻¹) for phytoplankton and ice algae. Spectral distribution of in situ absorption of light (m⁻¹) calculated as the absorption coefficient * fraction of PAR at the wavelength (a(λ) * I _f(λ)). The blue line is the normalized (PAR=1) spectrum below the ice.

Table 2 The absorption efficiency—A _e—(dimensionless) for ice algae and phyto-plankton at surface and under-ice light spectrum, respectively.

	Surface spectrum	Under-ice spectrum
Ice algae	1.00	0.90
Phytoplankton	0.96	1.04

Pope R.M., Fry E.S. Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements. Applied Optics. 1997; 36: 8710–8723.

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