Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO₂ levels

Abstract

A large-scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO 2 ) levels. At the start of the experiment, marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO 2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at~330 and~360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400-700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.

Altered inherent optical properties and estimates of the underwater light field during an Arctic under‐ice bloom of Phaeocystis pouchetii

“…[], who did not observe an initial increase in CDOM absorption even with a 100 times increase in Chl a concentration during a Phaeocystis bloom in the Southern Ocean. Weak correlation between Chl a and absorption by CDOM has also been previously reported in the Arctic Ocean [ Cota et al ., ; Wang et al ., ; Matsuoka et al ., ; Pavlov et al ., ]. The likely explanation is that CDOM pool in the water column accumulates over time and is controlled by combined biological, chemical and physical effects, not necessarily related to phytoplankton dynamics alone [ Nelson et al ., ; Wang et al ., ].…”

“…These optical properties include the relatively low a CDOM (375) values (Figure a), slope ratio ( S R , Figure c) above 1 [ Helms et al ., ], and a CDOM (375) versus S 300–650 relationship (Figure d) typical for autochtonous CDOM [cf., Stedmon and Markager , ]. Similar a CDOM (375) versus S 300–650 relationships have been previously observed in Atlantic‐dominated waters [ Pavlov et al ., ; Hancke et al ., ], contrary to a number of studies in regions influenced by terrestrial CDOM with weak or no dependence between spectral slope and CDOM absorption values [e.g., Granskog et al ., ].…”

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

“…6). This is similar to that presented by Kowalczuk et al (2006) in the Baltic Sea and Pavlov et al (2014) in Kongsfjorden, West Spitsbergen. In our study almost all data points are within the Stedmon and Markager (2001) model limits (Fig.…”

Evolution of dissolved and particulate chromophoric materials during the VAHINE mesocosm experiment in the New Caledonian coral lagoon (south-west Pacific)

“…Studies dealing with the CDOM dynamics in the frame of mesocosm experiments remain limited so far and have been conducted merely in coastal-temperate or polar ecosystems (Rochelle-Newall et al, 1999Pavlov et al, 2014). This work highlights the spectral characteristics and the variability of dissolved and particulate chromophoric materials throughout a 23-day mesocosm experiment in a tropical, oligotrophic LNLC ecosystem in which N 2 fixers and picophytoplankton play an essential role.…”

“…Even though CDOM absorption spectra are usually featureless, some "shoulders" have been observed sporadically in the UV and visible spectral domains and attributed to the presence of dissolved absorbing pigments released by phytoplankton cells: mycosporine-like amino acids (MAAs) at 310-320 or at 330-360 nm, and phaeopigments or non-chlorin metal-free porphyrins at 410-420 nm (Whitehead and Vernet, 2000;Röttgers and Koch, 2012;Organelli et al, 2014;Pavlov et al, 2014). In contrast, absorption coefficients of phytoplankton [a φ (λ)] determined from natural samples commonly display two main peaks in the visible range, around 435-450 and 675 nm, attributable to its content in total chlorophyll a (TChl a = mono Chl a+ divinyl Chl a) (Lutz et al, 1996;Dupouy et al, 1997;Bricaud et al, 2004), but may also reveal other peaks or shoulders resulting from the presence of other pigments: MAAs at 325 nm , TChl b, TChl c and photoprotective carotenoids at 460-470 nm, photosynthetic carotenoids and photoprotective keto-carotenoids at 490 nm (Carreto, 1985;Stuart et al, 1998;Wozniak et al, 1999;Lohrenz et al, 2003) as well as phycoerythrin at 550 nm (Morel, 1997).…”