More Like this

1. Phosphate and Iron Control Global Surface Ocean Dissolved Organic Phosphorus Concentrations

   Liang, Zhou ; Letscher, Robert ; Knapp, Angela ( June 2021 , ASLO meeting 2021)

   null (Ed.)

   Dissolved organic phosphorus (DOP) has a dual role in the surface ocean as both a product of primary production and as an organic nutrient fueling primary production and nitrogen Fixation, especially in oligotrophic gyres. Though poorly constrained, understanding the geographic distribution and environmental controls of surface ocean DOP concentration is critical to estimating distributions and rates of primary production and nitrogen Fixation in the global ocean. Here we pair DOP concentration measurements with a metric of phosphate (PO43-) stress (P*), satellite-based chlorophyll a concentrations, and iron stress estimates to explore their relationship with upper 50 m DOP stocks. Our results show that PO43- and iron stress work together to control surface DOP concentrations at basin scales. SpeciFcally, upper 50 m DOP stocks decrease with increasing phosphate stress, while alleviated iron stress leads to either surface DOP accumulation or loss depending on PO43- availability. Our work suggests an interdependence between DOP concentration, inorganic nutrient ratios, and iron availability, and establishes a predictive framework for DOP distributions in the global surface ocean. 

   more » « less
2. Time of Emergence and Large Ensemble Intercomparison for Ocean Biogeochemical Trends

   https://doi.org/10.1029/2019GB006453  

   Schlunegger, Sarah ; Rodgers, Keith B. ; Sarmiento, Jorge L. ; Ilyina, Tatiana ; Dunne, John P. ; Takano, Yohei ; Christian, James R. ; Long, Matthew C. ; Frölicher, Thomas L. ; Slater, Richard ; et al ( August 2020 , Global Biogeochemical Cycles)

   Anthropogenically forced changes in ocean biogeochemistry are underway and critical for the ocean carbon sink and marine habitat. Detecting such changes in ocean biogeochemistry will require quantification of the magnitude of the change (anthropogenic signal) and the natural variability inherent to the climate system (noise). Here we use Large Ensemble (LE) experiments from four Earth system models (ESMs) with multiple emissions scenarios to estimate Time of Emergence (ToE) and partition projection uncertainty for anthropogenic signals in five biogeochemically important upper‐ocean variables. We find ToEs are robust across ESMs for sea surface temperature and the invasion of anthropogenic carbon; emergence time scales are 20–30 yr. For the biological carbon pump, and sea surface chlorophyll and salinity, emergence time scales are longer (50+ yr), less robust across the ESMs, and more sensitive to the forcing scenario considered. We find internal variability uncertainty, and model differences in the internal variability uncertainty, can be consequential sources of uncertainty for projecting regional changes in ocean biogeochemistry over the coming decades. In combining structural, scenario, and internal variability uncertainty, this study represents the most comprehensive characterization of biogeochemical emergence time scales and uncertainty to date. Our findings delineate critical spatial and duration requirements for marine observing systems to robustly detect anthropogenic change.

    

   more » « less
3. Diverse but uncertain responses of picophytoplankton lineages to future climate change

   https://doi.org/10.1002/lno.11951  

   Flombaum, Pedro ; Martiny, Adam C. ( October 2021 , Limnology and Oceanography)

   Climate change is projected to modify the physical and chemical environment of the ocean, but the quantitative impact on the distribution of phytoplankton groups is unclear. Most Earth System Models (ESMs) predict future declines of phytoplankton in low latitude waters, contradicting observations showing that picophytoplankton can reach high abundance in warm waters. Here, we used a historic and three climate scenarios along with quantitative niche models to projectProchlorococcus,Synechococcus, and picoeukaryotic phytoplankton distributions for the year 2100. First, we found global responses with up to 50% and 9% increase forProchlorococcusandSynechococcusabundances, respectively, and 8% decrease for picoeukaryotic phytoplankton. All groups increased in abundance at low latitude, andSynechococcusand picoeukaryotic phytoplankton showed bands of decreases and increases in mid‐ and high‐latitudes, respectively.Prochlorococcustemporal trends were consistent among ESMs and increased with the strength of the scenario, whileSynechococcusand picoeukaryotic phytoplankton showed mixed results. Second, we evaluated sources of uncertainty associated to future projections. The anthropogenic uncertainty, associated to climate scenarios, increased with time and was relevant forProchlorococcus. The environmental and biological uncertainty, associated to ESMs and niche models, respectively, represented the largest fraction but differed among lineages. Quantifying uncertainties is key because the predicted differences in the future distribution and abundance can have large‐scale consequences on ocean ecosystem functioning.

    

   more » « less
4. Contrasting Roles of DOP as a Source of Phosphorus and Energy for Marine Diazotrophs

   https://doi.org/10.3389/fmars.2022.923765  

   Filella, Alba ; Riemann, Lasse ; Van Wambeke, France ; Pulido-Villena, Elvira ; Vogts, Angela ; Bonnet, Sophie ; Grosso, Olivier ; Diaz, Julia M. ; Duhamel, Solange ; Benavides, Mar ( July 2022 , Frontiers in Marine Science)

   The oceanic dissolved organic phosphorus (DOP) pool is mainly composed of P-esters and, to a lesser extent, equally abundant phosphonate and P-anhydride molecules. In phosphate-limited ocean regions, diazotrophs are thought to rely on DOP compounds as an alternative source of phosphorus (P). While both P-esters and phosphonates effectively promote dinitrogen (N 2 ) fixation, the role of P-anhydrides for diazotrophs is unknown. Here we explore the effect of P-anhydrides on N 2 fixation at two stations with contrasting biogeochemical conditions: one located in the Tonga trench volcanic arc region (“volcano,” with low phosphate and high iron concentrations), and the other in the South Pacific Gyre (“gyre,” with moderate phosphate and low iron). We incubated surface seawater with AMP (P-ester), ATP (P-ester and P-anhydride), or 3polyP (P-anhydride) and determined cell-specific N 2 fixation rates, nifH gene abundance, and transcription in Crocosphaera and Trichodesmium . Trichodesmium did not respond to any DOP compounds added, suggesting that they were not P-limited at the volcano station and were outcompeted by the low iron conditions at the gyre station. Conversely, Crocosphaera were numerous at both stations and their specific N 2 fixation rates were stimulated by AMP at the volcano station and slightly by 3polyP at both stations. Heterotrophic bacteria responded to ATP and 3polyP additions similarly at both stations, despite the contrasting phosphate and iron availability. The use of 3polyP by Crocosphaera and heterotrophic bacteria at both low and moderate phosphate concentrations suggests that this compound, in addition to being a source of P, can be used to acquire energy for which both groups compete. P-anhydrides may thus leverage energy restrictions to diazotrophs in the future stratified and nutrient-impoverished ocean. 

   more » « less
5. Alternate History: A Synthetic Ensemble of Ocean Chlorophyll Concentrations

   https://doi.org/10.1029/2020GB006924  

   Elsworth, Geneviève W. ; Lovenduski, Nicole S. ; McKinnon, Karen A. ( September 2021 , Global Biogeochemical Cycles)

   Internal climate variability plays an important role in the abundance and distribution of phytoplankton in the global ocean. Previous studies using large ensembles of Earth system models (ESMs) have demonstrated their utility in the study of marine phytoplankton variability. These ESM large ensembles simulate the evolution of multiple alternate realities, each with a different phasing of internal climate variability. However, ESMs may not accurately represent real world variability as recorded via satellite and in situ observations of ocean chlorophyll over the past few decades. Observational records of surface ocean chlorophyll equate to a single ensemble member in the large ensemble framework, and this can cloud the interpretation of long‐term trends: are they externally forced, caused by the phasing of internal variability, or both? Here, we use a novel statistical emulation technique to place the observational record of surface ocean chlorophyll into the large ensemble framework. Much like a large initial condition ensemble generated with an ESM, the resulting synthetic ensemble represents multiple possible evolutions of ocean chlorophyll concentration, each with a different sampling of internal climate variability. We further demonstrate the validity of our statistical approach by recreating an ESM ensemble of chlorophyll using only a single ESM ensemble member. We use the synthetic ensemble to explore the interpretation of long‐term trends in the presence of internal variability and find a wider range of possible trends in chlorophyll due to the sampling of internal variability in subpolar regions than in subtropical regions.

    

   more » « less