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Using fluorescent dissolved organic matter to trace and distinguish the origin of Arctic surface waters

View Article: PubMed Central - PubMed

ABSTRACT

Climate change affects the Arctic with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Fram and Davis Straits represent the major gateways connecting the Arctic and Atlantic. Oceanographic surveys were performed in the Fram and Davis Straits, and on the east Greenland Shelf (EGS), in late summer 2012/2013. Meteoric (fmw), sea-ice melt, Atlantic and Pacific water fractions were determined and the fluorescence properties of dissolved organic matter (FDOM) were characterized. In Fram Strait and EGS, a robust correlation between visible wavelength fluorescence and fmw was apparent, suggesting it as a reliable tracer of polar waters. However, a pattern was observed which linked the organic matter characteristics to the origin of polar waters. At depth in Davis Strait, visible wavelength FDOM was correlated to apparent oxygen utilization (AOU) and traced deep-water DOM turnover. In surface waters FDOM characteristics could distinguish between surface waters from eastern (Atlantic + modified polar waters) and western (Canada-basin polar waters) Arctic sectors. The findings highlight the potential of designing in situ multi-channel DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region without laborious samples analyses.

No MeSH data available.


Related in: MedlinePlus

T-S diagram and correlations between salinity and C1 in the east of Greenland.(a) Temperature (°C) vs. salinity with colorbar indicating C1 (R.U.) for all the samples collected in the eastern Greenland cruises. (b–d) Salinity vs. C1 (R.U.) and fpw as colorbar for polar waters and ASW for each of the eastern Greenland cruises. Black solid line (I) indicates the mixing curve for the polar waters (based on Fram 2012 and 2013 datasets). Gray dashed lines (II and III) indicate the two distinct mixing curves of polar waters over the Greenland shelf. The regressions were obtained by combining the three datasets. (I) y = –0.02 *(Sal) + 0.723, r2 = 0.90, p < 0.0001, n = 240. (II) y = 0.0042 *(Sal) − 0.0698, r2 = 0.90, p < 0.0001, n = 126. (III) y = 0.0183 *(Sal) −0.4816, r2 = 0.98, p < 0.0001, n = 18.
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f6: T-S diagram and correlations between salinity and C1 in the east of Greenland.(a) Temperature (°C) vs. salinity with colorbar indicating C1 (R.U.) for all the samples collected in the eastern Greenland cruises. (b–d) Salinity vs. C1 (R.U.) and fpw as colorbar for polar waters and ASW for each of the eastern Greenland cruises. Black solid line (I) indicates the mixing curve for the polar waters (based on Fram 2012 and 2013 datasets). Gray dashed lines (II and III) indicate the two distinct mixing curves of polar waters over the Greenland shelf. The regressions were obtained by combining the three datasets. (I) y = –0.02 *(Sal) + 0.723, r2 = 0.90, p < 0.0001, n = 240. (II) y = 0.0042 *(Sal) − 0.0698, r2 = 0.90, p < 0.0001, n = 126. (III) y = 0.0183 *(Sal) −0.4816, r2 = 0.98, p < 0.0001, n = 18.

Mentions: The T-S diagram (Fig. 6a) shows a clear distinction of polar waters exiting the Arctic, with respect to C1. Highest C1 fluorescence was associated with polar waters and ASW. The latter had comparatively lower values, indicating the dilution of surface waters by sea-ice melt and precipitation (glacial input and snow). The correlation of C1 with both temperature (not shown) and salinity (Fig. 6b–d) presented a very similar, however tighter, pattern than portrayed by absorption alone1033. When considering the salinity versus C1 relation for each cruise individually (except for Davis Strait), two distinct mixing curves for the dilution of polar waters are apparent (Fig. 6). C1 was also strongly inversely correlated to fsim (Figure S3) linking the high DOM signal to brine. In Davis Strait, different patterns were observed. The relationships C1 and C2 vs. salinity indicate two mixing curves (Fig. 7) in agreement with the mixing curves visible on the T-S diagram (Fig. 7a,b), where a clear separation of stations from eastern and western Davis Strait is apparent. The correlation between C1 and C2 in the East Greenland data could be harnessed tested if the FDOM in the Davis Strait had the same characteristics (relative proportions of C1 and C2) and hence similar origins. A regression was derived for C1 fluorescence based on C2 considering all the surface data (<200 m). This was then applied to the Davis Strait data to predict expected C1 fluorescence, C1*, for the surface layer in Davis Strait. The difference between measured and predicted C1 fluorescence, C1–C1*, is plotted against C2 (Fig. 7d) and indicates significant differences (p < 0.05) between eastern and western Davis Strait DOM. Samples in eastern Davis Strait have similar properties to those from the Fram Strait, whereas on the Canadian side of the strait the DOM has comparatively less C1. Finally for Davis Strait deep waters (>300 m), C1 was highly correlated with AOU, with the highest values of both parameters in BBDW (Fig. 4g,i). C2 showed no indication of elevated values at depth (Fig. 4h).


Using fluorescent dissolved organic matter to trace and distinguish the origin of Arctic surface waters
T-S diagram and correlations between salinity and C1 in the east of Greenland.(a) Temperature (°C) vs. salinity with colorbar indicating C1 (R.U.) for all the samples collected in the eastern Greenland cruises. (b–d) Salinity vs. C1 (R.U.) and fpw as colorbar for polar waters and ASW for each of the eastern Greenland cruises. Black solid line (I) indicates the mixing curve for the polar waters (based on Fram 2012 and 2013 datasets). Gray dashed lines (II and III) indicate the two distinct mixing curves of polar waters over the Greenland shelf. The regressions were obtained by combining the three datasets. (I) y = –0.02 *(Sal) + 0.723, r2 = 0.90, p < 0.0001, n = 240. (II) y = 0.0042 *(Sal) − 0.0698, r2 = 0.90, p < 0.0001, n = 126. (III) y = 0.0183 *(Sal) −0.4816, r2 = 0.98, p < 0.0001, n = 18.
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Related In: Results  -  Collection

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f6: T-S diagram and correlations between salinity and C1 in the east of Greenland.(a) Temperature (°C) vs. salinity with colorbar indicating C1 (R.U.) for all the samples collected in the eastern Greenland cruises. (b–d) Salinity vs. C1 (R.U.) and fpw as colorbar for polar waters and ASW for each of the eastern Greenland cruises. Black solid line (I) indicates the mixing curve for the polar waters (based on Fram 2012 and 2013 datasets). Gray dashed lines (II and III) indicate the two distinct mixing curves of polar waters over the Greenland shelf. The regressions were obtained by combining the three datasets. (I) y = –0.02 *(Sal) + 0.723, r2 = 0.90, p < 0.0001, n = 240. (II) y = 0.0042 *(Sal) − 0.0698, r2 = 0.90, p < 0.0001, n = 126. (III) y = 0.0183 *(Sal) −0.4816, r2 = 0.98, p < 0.0001, n = 18.
Mentions: The T-S diagram (Fig. 6a) shows a clear distinction of polar waters exiting the Arctic, with respect to C1. Highest C1 fluorescence was associated with polar waters and ASW. The latter had comparatively lower values, indicating the dilution of surface waters by sea-ice melt and precipitation (glacial input and snow). The correlation of C1 with both temperature (not shown) and salinity (Fig. 6b–d) presented a very similar, however tighter, pattern than portrayed by absorption alone1033. When considering the salinity versus C1 relation for each cruise individually (except for Davis Strait), two distinct mixing curves for the dilution of polar waters are apparent (Fig. 6). C1 was also strongly inversely correlated to fsim (Figure S3) linking the high DOM signal to brine. In Davis Strait, different patterns were observed. The relationships C1 and C2 vs. salinity indicate two mixing curves (Fig. 7) in agreement with the mixing curves visible on the T-S diagram (Fig. 7a,b), where a clear separation of stations from eastern and western Davis Strait is apparent. The correlation between C1 and C2 in the East Greenland data could be harnessed tested if the FDOM in the Davis Strait had the same characteristics (relative proportions of C1 and C2) and hence similar origins. A regression was derived for C1 fluorescence based on C2 considering all the surface data (<200 m). This was then applied to the Davis Strait data to predict expected C1 fluorescence, C1*, for the surface layer in Davis Strait. The difference between measured and predicted C1 fluorescence, C1–C1*, is plotted against C2 (Fig. 7d) and indicates significant differences (p < 0.05) between eastern and western Davis Strait DOM. Samples in eastern Davis Strait have similar properties to those from the Fram Strait, whereas on the Canadian side of the strait the DOM has comparatively less C1. Finally for Davis Strait deep waters (>300 m), C1 was highly correlated with AOU, with the highest values of both parameters in BBDW (Fig. 4g,i). C2 showed no indication of elevated values at depth (Fig. 4h).

View Article: PubMed Central - PubMed

ABSTRACT

Climate change affects the Arctic with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Fram and Davis Straits represent the major gateways connecting the Arctic and Atlantic. Oceanographic surveys were performed in the Fram and Davis Straits, and on the east Greenland Shelf (EGS), in late summer 2012/2013. Meteoric (fmw), sea-ice melt, Atlantic and Pacific water fractions were determined and the fluorescence properties of dissolved organic matter (FDOM) were characterized. In Fram Strait and EGS, a robust correlation between visible wavelength fluorescence and fmw was apparent, suggesting it as a reliable tracer of polar waters. However, a pattern was observed which linked the organic matter characteristics to the origin of polar waters. At depth in Davis Strait, visible wavelength FDOM was correlated to apparent oxygen utilization (AOU) and traced deep-water DOM turnover. In surface waters FDOM characteristics could distinguish between surface waters from eastern (Atlantic&thinsp;+&thinsp;modified polar waters) and western (Canada-basin polar waters) Arctic sectors. The findings highlight the potential of designing in situ multi-channel DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region without laborious samples analyses.

No MeSH data available.


Related in: MedlinePlus