Archive for DOM

Coastal DOM database – CoastDOM v1

Posted by hbenway 
· Wednesday, February 28th, 2024 

We present the first edition of a global database (CoastDOM v1) and a resulting data manuscript, which compiles previously published and unpublished measurements of DOC, DON, and DOP in coastal waters, consisting of 62,338 (DOC), 20,356 (DON), and 13,533 (DOP) data points, respectively.

CoastDOM v1 includes observations of concentrations from all continents between 1978 and 2022. However, most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the Southern Hemisphere.

This dataset will be useful for identifying global spatial and temporal patterns in DOM and will help facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochemical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing a baseline for modelling future changes in coastal waters.

The aim is to publish an updated version of the database periodically to determine global trends of DOM levels in coastal waters, and so if you have DOM data lying around, please submit it to Christian Lønborg (c.lonborg@ecos.au.dk).

CITATIONS

Lønborg et al. 2024. A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v1), Earth Syst. Sci. Data, 16, 1107–1119, https://doi.org/10.5194/essd-16-1107-2024

Lønborg et al. 2023.A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v.1). PANGAEA, https://doi.org/10.1594/PANGAEA.964012

Severe warming = 15% increase in bacterial respiration: Southern Ocean most impacted

Posted by mmaheigan 
· Thursday, March 30th, 2023 

The utilization, respiration, and remineralization of organic matter exported from the ocean surface to its depths are key processes in the ocean carbon cycle. Marine heterotrophic Bacteria play a critical role in these activities. However, most three-dimensional (3-D) coupled physical-biogeochemical models do not explicitly include Bacteria as a state variable. Instead, they rely on parameterization to account for the bacteria’s impact on particle flux attenuation.

A recent study examined how bacteria respond to climate change by employing a 3-D coupled ocean biogeochemical model that incorporates explicit bacterial dynamics. The model (CMCC-ESM2) is a part of the Coupled Model Intercomparison Project Phase 6. The authors first evaluated the reliability of century-scale forecasts (2015-2099) for bacterial stocks and rates in the upper 100 m layer against the compiled measurements from the contemporary period (1988-2011). Next the authors analyzed the predicted trends in bacterial stocks and rates under diverse climate scenarios and explored their association with regional differences in temperature and organic carbon stocks. Three crucial findings were revealed. There is a global-scale decrease in bacterial biomass of 5-10%, with a 3-5% increase in the Southern Ocean (Figure 1). In the Southern Ocean, the rise in semi-labile dissolved organic carbon (DOC) leads to an increase in DOC uptake rates of free-living bacteria; in the northern high and low latitudes, the increase in temperature drives the increase in their DOC uptake rates. Importantly, extreme warming could result in a global increase (up to 15%) and even higher in the Southern Ocean (21% increase) in bacterial respiration (Figure 1), potentially leading to a decline in the biological carbon pump.

This analysis is an unprecedented and early effort to understand the climate-induced changes in bacterial dynamics on a global scale in a systematic manner. This study takes us one step closer to comprehending how bacteria influence the functioning of the biological carbon pump and the distribution of organic carbon pools between surface and deep layers, especially their response to climate change.

Figure 1. Global projections of bacterial carbon stocks and rates during the baseline period (1990-2013) and their changes as anomalies under the most-severe climate change scenario (i.e., SSP5-8.5) relative to the baseline period (2076-2099). The stocks and rates during the baseline period (a, b, c, g, h, i) and their changes as anomalies under the most-severe climate change scenario (d, e, f, j, k, l). All variables are depth-integrated in the upper 100 m. Solid-line contours as standard deviation from averaging over 1990-2013. Anomalies are 2076-2099 average values relative to 1990-2013 average values. Global bacterial biomass has decreased by 5-10%, with a 3-5% increase in the Southern Ocean. However, extreme warming may increase bacterial respiration worldwide, thereby reducing the efficiency of the biological carbon pump. This study provides an early attempt to understand the response of bacteria to climate change and their impact on the distribution of organic carbon in the ocean.

 

Author
Heather Kim, Woods Hole Oceanographic Institution

How does the competition between phytoplankton and bacteria for iron alter ocean biogeochemical cycles?

Posted by mmaheigan 
· Friday, August 26th, 2022 

Free-living bacteria play a key role in cycling essential biogeochemical resources in the ocean, including iron, via their uptake, transformation, and release of organic matter throughout the water column. Bacteria process half of the ocean’s primary production, remineralize dissolved organic matter, and re-direct otherwise lost organic matter to higher trophic levels. For these reasons, it is crucial to understand what factors limit the growth of bacteria and how bacteria activities impact global ocean biogeochemical cycles.

In a recent study, Pham and colleagues used a global ocean ecosystem model to dive into how iron limits the growth of free-living marine bacteria, how bacteria modulate ocean iron cycling, and the consequences to marine ecosystems of the competition between bacteria and phytoplankton for iron.

Figure 1: (a) Iron limitation status of bacteria in December, January, and February (DJF) in the surface ocean. Low values (in blue color = close to zero) mean that iron is the limiting factor for the growth of bacteria; (b) Bacterial iron consumption in the upper 120m of the ocean and (c) Changes (anomalies) in export carbon production when bacteria have a high requirement for iron.

Through a series of computer simulations performed in the global ocean ecosystem model, the authors found that iron is a limiting factor for bacterial growth in iron-limited regions in the Southern Ocean, the tropical, and the subarctic Pacific due to the high iron requirement and iron uptake capability of bacteria. Bacteria act as an iron sink in the upper ocean due to their significant iron consumption, a rate comparable to phytoplankton. The competition between bacteria and phytoplankton for iron alters phytoplankton bloom dynamics, ocean carbon export, and the availability of dissolved organic carbon needed for bacterial growth. These results suggest that earth system models that omit bacteria ignore an important organism modulating biogeochemical responses of the ocean to future changes.

Authors: 
Anh Le-Duy Pham (Laboratoire d’Océanographie et de Climatologie: Expérimentation et Approches Numériques (LOCEAN), IPSL, CNRS/UPMC/IRD/MNHN, Paris, France)
Olivier Aumont (Laboratoire d’Océanographie et de Climatologie: Expérimentation et Approches Numériques (LOCEAN), IPSL, CNRS/UPMC/IRD/MNHN, Paris, France)
Lavenia Ratnarajah (University of Liverpool, United Kingdom)
Alessandro Tagliabue (University of Liverpool, United Kingdom)

Water clarity impacts temperature and biogeochemistry in Chesapeake Bay

Posted by mmaheigan 
· Thursday, December 3rd, 2020 

Estuarine water clarity is determined by suspended materials in the water, including colored dissolved organic matter, phytoplankton, sediment, and detritus. These constituents directly affect temperature because when water is opaque, sunlight heats only the shallowest layers near the surface, but when water is clear, sunlight can penetrate deeper, warming the waters below the surface. Despite the importance of accurately predicting temperature variability, many numerical modeling studies do not adequately parameterize this fundamental relationship between water clarity and temperature.

In a recent study published in Estuaries and Coasts, the authors quantified the impact of a more realistic representation of water clarity in a hydrodynamic-biogeochemical model of the Chesapeake Bay by comparing two simulations: (1) water clarity is constant in space and time for the calculation of solar heating vs. (2) water clarity varies with modeled concentrations of light-attenuating materials. In the variable water clarity simulation (2), the water is more opaque, particularly in the northern region of the Bay. During the spring and summer months, the lower water clarity in the northern Bay is associated with warmer surface temperatures and colder bottom temperatures. Warmer surface temperatures encourage phytoplankton growth and nutrient uptake near the head of the Bay, thus fewer nutrients are transported downstream. These conditions are exacerbated during high-river flow years, when differences in temperature, nutrients, phytoplankton, and zooplankton extend further seaward.

Figure 1: Top row: Difference in the light attenuation coefficient for shortwave heating, kh[m-1] (variable minus constant light attenuation simulation). June, July, and August average for (A) 2001, (B) average of 2001-2005, and (C) 2003; difference in bottom temperatures [oC] (variable minus constant). Bottom row: Difference in June, July, and August average bottom temperature for (D) 2001, (E) average of 2001-2005, and (F) 2003. Data for 2001 are representative of low river discharge, and 2003 are representative high river discharge years.

This work demonstrates that a constant light attenuation scheme for heating calculations in coupled hydrodynamic-biogeochemical models underestimates temperature variability, both temporally and spatially. This is an important finding for researchers who use models to predict future temperature variability and associated impacts on biogeochemistry and species habitability.

 

Authors:
Grace E. Kim (NASA, Goddard Space Flight Center)
Pierre St-Laurent (VIMS, William & Mary)
Marjorie A.M. Friedrichs (VIMS, William & Mary)
Antonio Mannino (NASA, Goddard Space Flight Center)

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