Impact of ocean acidification on phytoplankton assemblage, growth, and DMS production following Fe-dust additions in the NE Pacific high-nutrient, low-chlorophyll waters

Abstract

Abstract. Ocean acidification (OA) is likely to have an effect on the fertilizing potential of desert dust in high-nutrient, low-chlorophyll oceanic regions, either by modifying iron (Fe) speciation and bioavailability or by altering phytoplankton Fe requirements and acquisition. To address this issue, short incubations (4 days) of northeast subarctic Pacific waters enriched with either FeSO4 or dust and set at pH 8.0 (in situ) and 7.8 were conducted in August 2010. We assessed the impact of a decrease in pH on dissolved Fe concentration, phytoplankton biomass, taxonomy and productivity, and the production of dimethylsulfide (DMS) and its algal precursor dimethylsulfoniopropionate (DMSP). Chlorophyll a (chl a) remained unchanged in the controls and doubled in both the FeSO4-enriched and dust-enriched incubations, confirming the Fe-limited status of the plankton assemblage during the experiment. In the acidified treatments, a significant reduction (by 16–38 %) in the final concentration of chl a was measured compared to their nonacidified counterparts, and a 15 % reduction in particulate organic carbon (POC) concentration was measured in the dust-enriched acidified treatment compared to the dust-enriched nonacidified treatment. FeSO4 and dust additions had a fertilizing effect mainly on diatoms and cyanobacteria as estimated from algal pigment signatures. Lowering the pH affected mostly the haptophytes, but pelagophyte concentrations were also reduced in some acidified treatments. Acidification did not significantly alter DMSP and DMS concentrations. These results show that dust deposition events in a low-pH iron-limited northeast subarctic Pacific are likely to stimulate phytoplankton growth to a lesser extent than in today's ocean during the few days following fertilization and point to a low initial sensitivity of the DMSP and DMS dynamics to OA.

Iron sources alter the response of Southern Ocean phytoplankton to ocean acidification

“…1d−f), thus confirming that Fe-limitation was relieved and phytoplankton growth was stimulated through addition of either FeCl 3 or dust. In fact, enrichment by dust showed similar trends in F v /F m relative to FeCl 3 amendment irrespective of the pCO 2 , suggesting that dust can successfully relieve Fe-limitation, as previously observed (Mélancon et al 2016, Conway et al 2016. Accordingly, total dFe concentrations increased initially after Fe enrichment (dust and FeCl 3 ) whereas no significant differ-ences in total dFe were observed at the end of the first phase (Table 1).…”

“…Furthermore, similar total dFe concentrations were measured within the respective Fe treatments under both pCO 2 levels (Table 1), even for the dust treatment, supporting previous observations that the effect of OA on Fe(III)' solubility is rather small in seawater over the pH range of 7.5 to 9 (Kuma et al 1996, Liu & Millero 2002, Fishwick et al 2014. Hence, our results suggest that Fe solubility associated with dust was not significantly enhanced under OA as previously ob served (Fishwick et al 2014, Mélancon et al 2016. Previous studies, however, reported changes in Fe(III) complexation, resulting in a decline in the bioavailability of Fe(III) to marine phytoplankton (Shi et al 2010, Sugie et al 2013.…”

Impact of dust addition on Mediterranean plankton communities under present and future conditions of pH and temperature: an experimental overview

“…The study by Louis et al (2018), carried out with filtered (0.2 µm mesh size) natural seawater using the same dust analogue and flux as in the present study, showed that even an extreme ocean acidification scenario (∼ −0.6 pH units) does not impact the bioavailability of macro-and micro-nutrients (NO x , DIP and DFe) in the oligotrophic northwestern Mediterranean Sea. Similar results were found by Mélançon et al (2016) in high-nutrient lowchlorophyll (HNLC) waters of the northeastern Pacific, under a moderate ocean acidification scenario (−0.2 pH units). As no differences were observed for NO x and DIP concentrations within a few hours following dust addition under present and future environmental conditions, our results agree with these previous findings and further highlight the absence of a direct effect of ocean warming (+3 • C) on the release of nutrients from atmospheric particles.…”

“…Atmospheric deposition is well recognized as a significant source of micro-and macro-nutrients for surface waters of the global ocean (Duce et al, 1991;Jickells et al, 2005;Moore et al, 2013). The potential modulation of the biological carbon pump efficiency and the associated export of carbon by atmospheric deposition events are still poorly understood and quantified (Law et al, 2013).…”

Response of Microbial Communities on Culturing Plates of Post-settlement Sea Cucumbers to Seawater Acidification and Warming

“…For instance, previous studies found that acidification could decrease the postfertilization success and affect the growth, development, and physiological energetics of sea cucumbers (Yuan et al, 2015(Yuan et al, , 2016. Moreover, seawater acidification changes the seawater carbonate system, which could affect the marine ecological environment (Orr et al, 2005;Jian et al, 2019), and thus affect the marine primary productivity and community structure (Josiane et al, 2016) and the microbial composition and function (Lidbury et al, 2012;Kerfahi et al, 2020). Previous studies indicate that increased temperature is a driving abiotic factor in reshaping bacterial communities in the marine ecosystem (Smale et al, 2017;Mensch et al, 2020).…”