@article{fdi:010062557, title = {{C}ontrasted {S}aharan dust events in {LNLC} environments : impact on nutrient dynamics and primary production}, author = {{R}idame, {C}. and {D}ekaezemacker, {J}. and {G}uieu, {C}. and {B}onnet, {S}ophie and {L}'{H}elguen, {S}. and {M}alien, {F}.}, editor = {}, language = {{ENG}}, abstract = {{T}he response of the phytoplanktonic community (primary production and algal biomass) to contrasted {S}aharan dust events (wet and dry deposition) was studied in the framework of the {DUNE} ("a {DU}st experiment in a low-{N}utrient, low-chlorophyll {E}cosystem") project. {W}e simulated realistic dust deposition events (10 gm(-2)) into large mesocosms (52m(3)). {T}hree distinct dust addition experiments were conducted in {J}une 2008 ({DUNE}-1-{P}: simulation of a wet deposition; {DUNE}-1-{Q}: simulation of a dry deposition) and 2010 ({DUNE}-2-{R}1 and {DUNE}-2-{R}2: simulation of two successive wet depositions) in the northwestern oligotrophic {M}editerranean {S}ea. {N}o changes in primary production ({PP}) and chlorophyll a concentrations ({C}hl a) were observed after a dry deposition event, while a wet deposition event resulted in a rapid (24 h after dust addition), strong (up to 2.4-fold) and long (at least a week in duration) increase in {PP} and {C}hl a. {W}e show that, in addition to being a source of dissolved inorganic phosphorus ({DIP}), simulated wet deposition events were also a significant source of nitrate ({NO}3-) (net increases up to +9.8 mu {M} {NO}3- at 0.1m in depth) to the nutrient-depleted surface waters, due to cloud processes and mixing with anthropogenic species such as {HNO}3. {T}he dry deposition event was shown to be a negligible source of {NO}3-. {B}y transiently increasing {DIP} and {NO}3- concentrations in {N}-{P} starved surface waters, wet deposition of {S}aharan dust was able to relieve the potential {N} or {NP} co-limitation of the phytoplanktonic activity. {D}ue to the higher input of {NO}3- relative to {DIP}, and taking into account the stimulation of the biological activity, a wet deposition event resulted in a strong increase in the {NO}3-/{DIP} ratio, from initially less than 6, to over 150 at the end of the {DUNE}-2-{R}1 experiment, suggesting a switch from an initial {N} or {NP} co-limitation towards a severe {P} limitation. {W}e also show that the contribution of new production to {PP} strongly increased after wet dust deposition events, from initially 15% to 60-70% 24 h after seeding, indicating a switch from a regenerated-production based system to a new-production based system. {DUNE} experiments show that wet and dry dust deposition events induce contrasting responses of the phytoplanktonic community due to differences in the atmospheric supply of bioavailable new nutrients. {O}ur results from original mesocosm experiments demonstrate that atmospheric dust wet deposition greatly influences primary productivity and algal biomass in {LNLC} environments through changes in the nutrient stocks, and alters the {NO}3-/{DIP} ratio, leading to a switch in the nutrient limitation of the phytoplanktonic activity.}, keywords = {{MEDITERRANEE} ; {SAHARA}}, booktitle = {}, journal = {{B}iogeosciences}, volume = {11}, numero = {17}, pages = {4783--4800}, ISSN = {1726-4170}, year = {2014}, DOI = {10.5194/bg-11-4783-2014}, URL = {https://www.documentation.ird.fr/hor/fdi:010062557}, }