Archive for bloom – Page 2

When marine-terminating glaciers ‘pump’ the ocean

Posted by mmaheigan 
· Wednesday, October 10th, 2018 

How will increasing meltwater from Greenland affect the biogeochemistry of the ocean? Release of meltwater into the ocean has physical and biogeochemical effects on the local water column. With respect to nutrient availability, meltwater supplies the bioessential nutrients iron and silicic acid but is deficient in nitrate and phosphate. However, despite very low meltwater nitrate and phosphate concentrations, pronounced summertime phytoplankton blooms are observed in many, though not all, of Greenland’s large fjord systems. These unusual summertime blooms are associated with meltwater from marine-terminating glaciers. So if the meltwater itself is not supplying nitrate and phosphate that these blooms require, what is the source of the nutrients that support these blooms?

An illustration of how changing the depth of a glacier affects downstream productivity

A recent study published in Nature Communications shows that when meltwater is released below sea level under large marine-terminating glaciers, it rises rapidly towards the surface in buoyant discharge plumes. As these plumes rise, they entrain large quantities of deep, nutrient-rich seawater. This vertical transport, or ‘pumping’, of these nutrients to the surface sustains unusually high summertime productivity in Greenland’s fjords. Conversely, when meltwater is released at the ocean surface, primary production is reduced because the meltwater itself lacks the nitrate and phosphate required to fuel phytoplankton blooms. Consequently, the inland retreat of Greenland’s large marine-terminating glaciers is ultimately bad news for summertime marine phytoplankton communities. As the depth of the marine-terminating glaciers shoals, their associated nutrient ‘pumps’ collapse, which will likely have negative effects on primary production and associated inshore fisheries.

 

Authors:
M.J. Hopwood (GEOMAR)
D. Carroll (Jet Propulsion Laboratory)
T.J. Browning (GEOMAR)
L. Meire (Royal Netherlands Institute for Sea Research and Greenland Climate Research Centre)
J. Mortensen (Greenland Climate Research Centre)
S. Krisch (GEOMAR)
E.P. Achterberg (GEOMAR)

Biophysical drivers of vigorous carbon cycling near the Kuroshio Extension

Posted by mmaheigan 
· Thursday, April 27th, 2017 

The Kuroshio Current and its Extension jet in the western North Pacific Ocean form a dynamic western boundary current (WBC) region characterized by large air-sea exchanges of heat and carbon dioxide gas (CO2). The jet is known to oscillate between stable and meandering states on multi-year timescales that alter the eddy field and depth of winter mixing in the southern recirculation gyre. These dynamic state changes have been shown to imprint biogeochemical signatures onto regional mode waters that can be distributed widely throughout the North Pacific and remain out of contact with the atmosphere for decades.

Figure. ~7 years of (a) AVISO daily sea surface height (SSH) anomalies and (b) upper-ocean temperature from the NOAA Kuroshio Extension Observatory (KEO) surface mooring. Black and gray lines in b show the mixed layer depth (MLD) and 17C contour, respectively. Spring bloom periods are indicated in blue in a. The semi-regular upwelling of cold water and corresponding depression of SSH is caused by cold-core eddies that pass the KEO mooring. Winter ventilation depths increase by ~100 m after 2010 when the extension jet entered a stable phase.

To better characterize carbon cycling in this region, ~7 years of daily-averaged autonomous CO2 observations from NOAA’s Kuroshio Extension Observatory (KEO) surface mooring were used to close the mixed layer carbon budget. High rates of net community production (NCP; >100 mmol C m-2 d-1) were observed during the spring bloom period, and a mean annual NCP of 7±3 mol C m-2 yr-1 was determined. Biological processes near KEO largely balance the input of carbon that occurs annually through winter mixing; however, physical processes that deviate from climatology were not resolved in this study. Therefore, it remains unclear how transient features such as eddies influence biological carbon production and export through altered nutrient supply and active vertical transport of organic material. Further work is required to determine how biophysical interactions during mesoscale and submesoscale disturbances contribute to local carbon cycle processes and variability in regional mode water carbon inventories.

Ocean Carbon Hot Spots, an upcoming workshop focused on understanding biophysical drivers of carbon uptake in WBC regions, will be held September 25-26, 2017 at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California. The primary objective of the workshop is to develop a community of observationalists and modelers working on the topic, and to identify critical observational needs that would improve model parameterizations. Ocean Carbon Hot Spots will be co-sponsored by US CLIVAR, US OCB, MBARI, and OMIX.

Written by Andrea J. Fassbender, Monterey Bay Aquarium Research Institute

 

Mixed-layer carbon cycling at the Kuroshio Extension Observatory (Global Biogeochemical Cycles) 

Authors:
Andrea J. Fassbender (Monterey Bay Aquarium Research Institute)
Christopher L. Sabine (NOAA Pacific Marine Environmental Laboratory)
Meghan F. Cronin (NOAA Pacific Marine Environmental Laboratory)
Adrienne J. Sutton (Joint Institute for the Study of the Atmosphere and Ocean, University of Washington)

Satellite Laser Lights Up Polar Research

Posted by mmaheigan 
· Thursday, April 13th, 2017 

What controls annual cycles and interannual changes in polar phytoplankton biomass? Answers to this question are now emerging from a satellite light detection and ranging (lidar) sensor, which can observe the polar oceans throughout the extensive periods when measurements from traditional passive ocean color sensors are impossible. The new study uses active lidar measurements from the CALIOP satellite sensor to construct complete decade-long record of phytoplankton biomass in the northern and southern polar regions. Results of the study show that annual cycles in biomass are driven by rates of acceleration and deceleration in phytoplankton division, with bloom termination coinciding with maximum division rates irrespective of whether nutrients are exhausted. The study further shows that interannual differences in bloom strength can be quantitatively related to the difference between the winter minimum to summer maximum in division rates. Finally, the analysis indicated that ecological processes had a greater impact than ice cover changes on integrated polar zone phytoplankton biomass in the north, whereas ice cover changes were the dominant driver in the south polar zone. Despite being designed for atmospheric research, CALIOP has provided the first demonstration that active satellite lidar measurements can yield important new insights on plankton ecology in the climate sensitive polar regions. This proof-of-concept creates a foundation for a future ocean-optimized sensor with water-column profiling capabilities that would launch a new lidar era in satellite oceanography.

 

 

Authors:

Michael J. Behrenfeld (Oregon State Univ.)
Yongxiang Hu (NASA Langley Research Center)
Robert T. O’Malley (Oregon State Univ.)
Emmanuel S. Boss (Univ. Maine)
Chris A. Hostetler (NASA Langley Research Center)
David A. Siegel (Univ. California Santa Barbara)
Jorge Sarmiento (Princeton Univ.)
Jennifer Schulien (Oregon State Univ.)
Johnathan W. Hair (NASA Langley Research Center)
Xiaomei Lu (NASA Langley Research Center)
Sharon Rodier (NASA Langley Research Center)
Amy Jo Scarino (NASA Langley Research Center)

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