Investigation into the impact of storms on sustaining summer primary productivity in the Sub‐Antarctic Ocean

Nicholson, Sarah; Lévy, Marina; Llort, Joan; Swart, Sebastiaan; Monteiro, Pedro M. S.

doi:10.1002/2016gl069973

Cited by 44 publications

(60 citation statements)

References 43 publications

(67 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, there is now compelling evidence to suggest that storm events may also play a critical role in extending the duration of summertime production through intra-seasonal entrainment of dissolved iron from a subsurface reservoir (Carranza and Gille, 2015;Fauchereau et al, 2011;Swart et al, 2015;Thomalla et al, 2011). This mechanism was tested using a 1-D biogeochemical model by Nicholson et al (2016) whose results suggest that intra-seasonal mixed-layer perturbations may offer relief from iron limitation in summer, particularly if there is sufficient subsurface vertical mixing beneath the surface mixed layer.…”

Section: Discussionmentioning

confidence: 99%

“…Tagliabue et al (2014) postulated that due to weak diapycnal inputs of iron, there must be a heavy reliance on Fe recycling within the mixed layer to meet the iron demand. An alternative hypothesis is that summer storms can sustain mixed-layer biomass through the entrainment of limiting nutrients, particularly in the SAZ (Carranza and Gille, 2015;Nicholson et al, 2016;Swart et al, 2015). As a storm passes through the SAZ, it deepens the mixed layer accessing the subsurface iron reservoir; the subsequent re-shoaling of this buoyant water fuels surface water phytoplankton growth in a high-light and replenished-nutrient environment.…”

Section: T J Ryan-keogh Et Al: Seasonal Development Of Iron Limitamentioning

confidence: 99%

“…The Atlantic sector of the Southern Ocean is composed of a series of water masses, each with distinct physical and chemical properties (Boyer et al, 2013), that are constrained by circumpolar fronts with large geostrophic velocities (Nowlin and Klinck, 1986;Orsi et al, 1995). The differing physical and chemical properties create a high degree of zonal variability within the biology, in particular regarding the timing and extent of phytoplankton seasonal blooms (Thomalla et al, 2011).…”

Section: T J Ryan-keogh Et Al: Seasonal Development Of Iron Limitamentioning

confidence: 99%

“…Nutrient addition incubation experiments were performed using methods similar to those employed previously in the Southern Ocean Nielsdóttir et al, 2012;Ryan-Keogh et al, 2017a) and the high-latitude North Atlantic (Ryan-Keogh et al, 2013). Water for experiments was transferred unscreened into an acid-washed 50 L LDPE carboy (Thermo Scientific) to ensure homogenization; the homogenized water was then redistributed unscreened into 2.4 L polycarbonate bottles (Nalgene) for the experiments.…”

Section: Nutrient Addition Incubation Experimentsmentioning

confidence: 99%

See 3 more Smart Citations

Seasonal development of iron limitation in the sub-Antarctic zone

Ryan‐Keogh

Thomalla

Mtshali³

et al. 2018

Biogeosciences

View full text Add to dashboard Cite

Abstract. The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ; ∼ 40-45 • S) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron availability is due to an interplay between winter entrainment, diapycnal diffusion, storm-driven entrainment, atmospheric deposition, iron scavenging and iron recycling processes. Biological observations utilizing grow-out iron addition incubation experiments were performed at different stages of the seasonal cycle within the SAZ to determine whether iron availability at the time of sampling was sufficient to meet biological demands at different times of the growing season. Here we demonstrate that at the beginning of the growing season, there is sufficient iron to meet the demands of the phytoplankton community, but that as the growing season develops the mean iron concentrations in the mixed layer decrease and are insufficient to meet biological demand. Phytoplankton increase their photosynthetic efficiency and net growth rates following iron addition from midsummer to late summer, with no differences determined during early summer, suggestive of seasonal iron depletion and an insufficient resupply of iron to meet biological demand. The result of this is residual macronutrients at the end of the growing season and the prevalence of the high-nutrient low-chlorophyll (HNLC) condition. We conclude that despite the prolonged growing season characteristic of the SAZ, which can extend into late summer/early autumn, results nonetheless suggest that iron supply mechanisms are insufficient to maintain potential maximal growth and productivity throughout the season.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: T J Ryan-keogh Et Al: Seasonal Development Of Iron Limitamentioning

confidence: 99%

Section: T J Ryan-keogh Et Al: Seasonal Development Of Iron Limitamentioning

confidence: 99%

Section: Nutrient Addition Incubation Experimentsmentioning

confidence: 99%

See 2 more Smart Citations

Seasonal development of iron limitation in the sub-Antarctic zone

Ryan‐Keogh

Thomalla

Mtshali³

et al. 2018

Biogeosciences

View full text Add to dashboard Cite

show abstract

“…Weak diapycnal inputs and a heavy reliance on iron recycling was suggested by Tagliabue et al (2014) to match approximate phytoplankton utilization within the pelagic zones. An alternative theory that postulates the importance of summer storms may also be pivotal in understanding the seasonal dynamics of phytoplankton primary productivity (Nicholson et al, 2016;Swart et al, 2015;Thomalla et al, 2015), with respect to the sustained bloom observed in the sub-Antarctic Zone (SAZ). Here, summer storms are said to periodically deepen the mixed layer to below the ferricline followed by rapid shoaling during quiescent periods that balances the supply of light and iron in the upper oceans favouring phytoplankton growth that culminates in a sustained summer bloom .…”

Section: Introductionmentioning

confidence: 99%

Modelled estimates of spatial variability of iron stress in the Atlantic sector of the Southern Ocean

Ryan‐Keogh

Thomalla²,

Mtshali³

et al. 2017

Biogeosciences

View full text Add to dashboard Cite

Abstract. The Atlantic sector of the Southern Ocean is characterized by markedly different frontal zones with specific seasonal and sub-seasonal dynamics. Demonstrated here is the effect of iron on the potential maximum productivity rates of the phytoplankton community. A series of iron addition productivity versus irradiance (PE) experiments utilizing a unique experimental design that allowed for 24 h incubations were performed within the austral summer of 2015/16 to determine the photosynthetic parameters α B , P B max and E k . Mean values for each photosynthetic parameter under iron-replete conditions were 1.46 ± 0.55 (µg (µg Chl a) −1 h −1 (µM photons m −2 s −1 ) −1 ) for α B , 72.55 ± 27.97 (µg (µg Chl a) −1 h −1 ) for P B max and 50.84 ± 11.89 (µM photons m −2 s −1 ) for E k , whereas mean values under the control conditions were 1.25 ± 0.92 (µg (µg Chl a) −1 h −1 (µM photons m −2 s −1 ) −1 ) for α B , 62.44 ± 36.96 (µg (µg Chl a) −1 h −1 ) for P B max and 55.81 ± 19.60 (µM photons m −2 s −1 ) for E k . There were no clear spatial patterns in either the absolute values or the absolute differences between the treatments at the experimental locations. When these parameters are integrated into a standard depth-integrated primary production model across a latitudinal transect, the effect of iron addition shows higher levels of primary production south of 50 • S, with very little difference observed in the subantarctic and polar frontal zone. These results emphasize the need for better parameterization of photosynthetic parameters in biogeochemical models around sensitivities in their response to iron supply. Future biogeochemical models will need to consider the combined and individual effects of iron and light to better resolve the natural background in primary production and predict its response under a changing climate.

show abstract

Low-frequency and high-frequency oscillatory winds synergistically enhance nutrient entrainment and phytoplankton at fronts

Whitt

Lévy

Taylor

2017

J. Geophys. Res. Oceans

View full text Add to dashboard Cite

When phytoplankton growth is limited by low nutrient concentrations, full‐depth‐integrated phytoplankton biomass increases in response to intermittent mixing events that bring nutrient‐rich waters into the sunlit surface layer. Here it is shown how oscillatory winds can induce intermittent nutrient entrainment events and thereby sustain more phytoplankton at fronts in nutrient‐limited oceans. Low‐frequency (i.e., synoptic to planetary scale) along‐front wind drives oscillatory cross‐front Ekman transport, which induces intermittent deeper mixing layers on the less dense side of fronts. High‐frequency wind with variance near the Coriolis frequency resonantly excites inertial oscillations, which also induce deeper mixing layers on the less dense side of fronts. Moreover, we show that low‐frequency and high‐frequency winds have a synergistic effect and larger impact on the deepest mixing layers, nutrient entrainment, and phytoplankton growth on the less dense side of fronts than either high‐frequency winds or low‐frequency winds acting alone. These theoretical results are supported by two‐dimensional numerical simulations of fronts in an idealized nutrient‐limited open‐ocean region forced by low‐frequency and high‐frequency along‐front winds. In these model experiments, higher‐amplitude low‐frequency wind strongly modulates and enhances the impact of the lower‐amplitude high‐frequency wind on phytoplankton at a front. Moreover, sensitivity studies emphasize that the synergistic phytoplankton response to low‐frequency and high‐frequency wind relies on the high‐frequency wind just below the Coriolis frequency.

show abstract

Investigation into the impact of storms on sustaining summer primary productivity in the Sub‐Antarctic Ocean

Cited by 44 publications

References 43 publications

Seasonal development of iron limitation in the sub-Antarctic zone

Seasonal development of iron limitation in the sub-Antarctic zone

Modelled estimates of spatial variability of iron stress in the Atlantic sector of the Southern Ocean

Low-frequency and high-frequency oscillatory winds synergistically enhance nutrient entrainment and phytoplankton at fronts

Contact Info

Product

Resources

About