scholarly journals Southern Ocean BGC-Argo Detect Under Ice Phytoplankton Growth Before Sea Ice Retreat

2020 ◽  
Author(s):  
Mark Hague ◽  
Marcello Vichi
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Light Adaptation ◽  
Data Sampling ◽  
Argo Data ◽  
Ice Melt ◽  
Antarctic Sea Ice ◽  
Highly Active ◽  
Ice Retreat ◽  
Ice Edge

Abstract. The seasonality of sea ice in the Southern Ocean has profound effects on the life cycle (phenology) of phytoplankton residing under the ice. The current literature investigating this relationship is primarily based on remote sensing, which often lacks data for half the year or more. One prominent hypothesis holds that following ice retreat in spring, buoyant melt waters enhance irradiance levels, triggering a bloom which follows the ice edge. However, an analysis of BGC-Argo data sampling under Antarctic sea ice suggests that this is not necessarily the case. Rather than precipitating rapid accumulation, we show that melt waters enhance growth in an already highly active phytoplankton population. Blooms observed in the wake of the receding ice edge can then be understood as the emergence of a growth process that started earlier under sea ice. Indeed, we estimate that growth initiation occurs, on average, 4–5 weeks before ice retreat, typically starting in August and September. Novel techniques using on-board data to detect the timing of ice melt were used. Furthermore, such growth is shown to occur under conditions of substantial ice cover (> 90 % satellite ice concentration) and deep mixed layers (> 100 m), conditions previously thought to be inimical to growth. This led to the development of several 0D model experiments in which we sought to investigate the mechanisms responsible for such early growth. The results of theses experiments suggest that a combination of higher light transfer (penetration) through sea ice and extreme low light adaptation by phytoplankton can account for the observed phenology.

scholarly journals Southern Ocean Biogeochemical Argo detect under-ice phytoplankton growth before sea ice retreat

2021 ◽  
Vol 18 (1) ◽  
pp. 25-38
Author(s):  
Mark Hague ◽  
Marcello Vichi
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Light Adaptation ◽  
Ice Cover ◽  
Data Sampling ◽  
Argo Data ◽  
Ice Melt ◽  
Antarctic Sea Ice ◽  
Ice Retreat ◽  
Ice Edge

Abstract. The seasonality of sea ice in the Southern Ocean has profound effects on the life cycle (phenology) of phytoplankton residing under the ice. The current literature investigating this relationship is primarily based on remote sensing, which often lacks data for half of the year or more. One prominent hypothesis holds that, following ice retreat in spring, buoyant meltwaters enhance available irradiance, triggering a bloom which follows the ice edge. However, an analysis of Biogeochemical Argo (BGC-Argo) data sampling under Antarctic sea ice suggests that this is not necessarily the case. Rather than precipitating rapid accumulation, we show that meltwaters enhance growth in an already highly active phytoplankton population. Blooms observed in the wake of the receding ice edge can then be understood as the emergence of a growth process that started earlier under sea ice. Indeed, we estimate that growth initiation occurs, on average, 4–5 weeks before ice retreat, typically starting in August and September. Novel techniques using on-board data to detect the timing of ice melt were used. Furthermore, such growth is shown to occur under conditions of substantial ice cover (>90 % satellite ice concentration) and deep mixed layers (>100 m), conditions previously thought to be inimical to growth. This led to the development of several box model experiments (with varying vertical depth) in which we sought to investigate the mechanisms responsible for such early growth. The results of these experiments suggest that a combination of higher light transfer (penetration) through sea ice cover and extreme low light adaptation by phytoplankton can account for the observed phenology.

scholarly journals DASSO: a data assimilation system for the Southern Ocean that utilizes both sea-ice concentration and thickness observations

2021 ◽  
pp. 1-6
Author(s):  
Hao Luo ◽  
Qinghua Yang ◽  
Longjiang Mu ◽  
Xiangshan Tian-Kunze ◽  
Lars Nerger ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Southern Ocean ◽  
Sea Ice ◽  
Coupled Model ◽  
Sea Ice Concentration ◽  
Model Free ◽  
Antarctic Sea Ice ◽  
Ice Concentration ◽  
Data Assimilation System ◽  
Assimilation System

Abstract To improve Antarctic sea-ice simulations and estimations, an ensemble-based Data Assimilation System for the Southern Ocean (DASSO) was developed based on a regional sea ice–ocean coupled model, which assimilates sea-ice thickness (SIT) together with sea-ice concentration (SIC) derived from satellites. To validate the performance of DASSO, experiments were conducted from 15 April to 14 October 2016. Generally, assimilating SIC and SIT can suppress the overestimation of sea ice in the model-free run. Besides considering uncertainties in the operational atmospheric forcing data, a covariance inflation procedure in data assimilation further improves the simulation of Antarctic sea ice, especially SIT. The results demonstrate the effectiveness of assimilating sea-ice observations in reconstructing the state of Antarctic sea ice, but also highlight the necessity of more reasonable error estimation for the background as well as the observation.

scholarly journals The Response of the Nordic Seas to Wintertime Sea-ice Retreat

2021 ◽  
pp. 1-40
Author(s):  
Yue Wu ◽  
David P. Stevens ◽  
Ian A. Renfrew ◽  
Xiaoming Zhai
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
Climate Model ◽  
Sea Temperature ◽  
Nordic Seas ◽  
Ocean Response ◽  
Marginal Ice Zone ◽  
Ice Retreat ◽  
Ice Edge ◽  
Sea Ice Retreat

AbstractThe ocean response to wintertime sea-ice retreat is investigated in the coupled climate model HiGEM. We focus on the marginal ice zone and adjacent waters of the Nordic Seas, where the air-sea temperature difference can be large during periods of off-ice winds promoting high heat flux events. Both control and transient climate model ensembles are examined, which allows us to isolate the ocean response due to sea-ice retreat from the response due to climate change. As the wintertime sea-ice edge retreats towards the Greenland coastline, it exposes waters that were previously covered by ice which enhances turbulent heat loss and mechanical mixing, leading to a greater loss of buoyancy and deeper vertical mixing in this location. However, under global warming, the buoyancy loss is inhibited as the atmosphere warms more rapidly than the ocean which reduces the air-sea temperature difference. This occurs most prominently further away from the retreating ice edge, over the Greenland Sea gyre. Over the gyre the upper ocean also warms significantly, resulting in a more stratified water column and, as a consequence, a reduction in the depth of convective mixing. In contrast, closer to the coast the effect of global warming is overshadowed by the effect of the sea-ice retreat, leading to significant changes in ocean temperature and salinity in the vicinity of the marginal ice zone.

Last Glacial Maximum Antarctic sea ice linked with global mean ocean temperature: evidence from PMIP3, PMIP4 and MIROC-4m simulations

2021 ◽  
Author(s):  
Tristan Vadsaria ◽  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Takashi Obase ◽  
Wing-Le Chan ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Ocean Temperature ◽  
Sea Ice Extent ◽  
Last Glacial ◽  
Antarctic Sea Ice ◽  
The Antarctic

<p>Southern Ocean sea ice and oceanic fronts are known to play an important role on the climate system, carbon cycles, bottom ocean circulation, and Antarctic ice sheet. However, many models of the previous Past-climate Model Intercomparison Project (PMIP) underestimated sea-ice extent (SIE) for the Last Glacial Maximum (LGM)(Roche et al., 2012; Marzocchi and Jensen, 2017), mainly because of surface bias (Flato et al., 2013) that may have an impact on mean ocean temperature (MOT). Indeed, recent studies further suggest an important link between Southern Ocean sea ice and mean ocean temperature (Ferrari et al., 2014; Bereiter et al., 2018 among others). Misrepresent the Antarctic sea-ice extent could highly impact deep ocean circulation, the heat transport and thus the MOT. In this study, we will stress the relationship between the distribution of Antarctic sea-ice extent and the MOT through the analysis of the PMIP3 and PMIP4 exercise and by using a set of MIROC models. To date, the latest version of MIROC improve its representation of the LGM Antarctic sea-ice extent, affecting the deep circulation and the MOT distribution (Sherriff-Tadano et al., under review).</p><p>Our results show that available PMIP4 models have an overall improvement in term of LGM sea-ice extent compared to PMIP3, associated to colder deep and bottom ocean temperature. Focusing on MIROC (4m) models, we show that models accounting for Southern Ocean sea-surface temperature (SST) bias correction reproduce an Antarctic sea-ice extent, 2D-distribution, and seasonal amplitude in good agreement with proxy-based data. Finally, using PMIP-MIROC analyze, we show that it exists a relationship between the maximum SIE and the MOT, modulated by the Antarctic intermediate and bottom waters.</p>

scholarly journals Characteristics of Altimetry Signatures Over Sea Ice (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 240
Author(s):  
N.F. McIntyre ◽  
S.W. Laxon
Keyword(s):  
Sea Ice ◽  
Continental Margin ◽  
Small Proportion ◽  
The Arctic ◽  
Antarctic Sea Ice ◽  
Surface Measurements ◽  
Characteristic Sequences ◽  
Data Coverage ◽  
Ice Edge

We report characteristics of Seasat altimetry signatures recorded over Antarctic sea ice. Up to four discrete zones can at times be seen in characteristic sequences in the Weddell and Ross Seas, and elsewhere. They are substantially larger than those reported in the Arctic, covering up to 2500 km at the time of maximum ice extent in 1978. Transitions between them can be abrupt, with marked changes occurring in less than a few kilometres. Some zones were found to persist through the 3 month satellite lifetime; others exhibited intermittent variations. Repeat data coverage has enabled temporal as well as spatial patterns to be investigated. Interpretation of the geophysical cause of the patterns observed has been limited by available data. Some comparisons may be made with surface measurements of nadir back-scatter on first- and multi-year floes but these account for only a small proportion of the altimetry returns studied. Correlations with the NOAA Navy Ice Charts show significant disparities in the determination of the ice edge which may relate to the sensitivity of the altimeter to the presence of fresh ice or ice in very small quantities. Similar signatures can be found next to small coastal leads at the continental margin, an area known to be important for the growth of new ice.

scholarly journals The Effect of Antarctic Sea Ice on Southern Ocean Carbon Outgassing: Capping Versus Light Attenuation

2020 ◽  
Vol 34 (8) ◽  
Author(s):  
Mukund Gupta ◽  
Michael J. Follows ◽  
Jonathan Maitland Lauderdale
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Light Attenuation ◽  
Antarctic Sea Ice ◽  
Ocean Carbon

scholarly journals Seasonal changes of sea-ice characteristics off East Antarctica

1994 ◽  
Vol 20 ◽  
pp. 195-201 ◽  
Author(s):  
Ian Allison ◽  
Anthony Worby
Keyword(s):  
Sea Ice ◽  
Ice Cores ◽  
Open Water ◽  
Ice Formation ◽  
Ice Thickness ◽  
Spatial And Temporal Variability ◽  
Growth Season ◽  
Ice Growth ◽  
Antarctic Sea Ice ◽  
Ice Edge

Data on Antarctic sea‐ice characteristics, and their spatial and temporal variability, are presented from cruises between 1986 and 1993 for the region spanning 60°−150° E between October and May. In spring, the sea‐ice zone is a variable mixture of different thicknesses of ice plus open water and in some regions only 30−40% of the area is covered with ice >0.3 m thick. The thin‐ice and open‐water areas are important for air‐sea heat exchange. Crystallographic analyses of ice cores, supported by salinity and stable‐isotope measurements, show that approximately 50% of the ice mass is composed of small frazil crystals. These are formed by rapid ice growth in leads and polynyas and indicate the presence of open water throughout the growth season. The area‐averaged thickness of undeformed ice west of 120° E is typically less than 0.3 m and tends to‐increase with distance south of the ice edge. Ice growth by congelation freezing rarely exceeds 0.4 m, with increases in ice thickness beyond this mostly attributable to rafting and ridging. While most of the total area is thin ice or open water, in the central pack much of the total ice mass is contained in ridges. Taking account of the extent of ridging, the total area‐averaged ice thickness is estimated to be about 1m for the region 60°−90° E and 2 m for the region 120°−150° E. By December, new ice formation has ceased in all areas of the pack and only floes >0.3 m remain. In most regions these melt completely over the summer and the new season's ice formation starts in late February. By March, the thin ice has reached a thickness of 0.15 0.30 m, with nilas formation being an important mechanism for ice growth within the ice edge

scholarly journals Impacts of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in the Goddard Earth Observing System, Version 5 (GEOS-5)

2016 ◽  
Vol 29 (9) ◽  
pp. 3199-3218 ◽  
Author(s):  
Feng Li ◽  
Yury V. Vikhliaev ◽  
Paul A. Newman ◽  
Steven Pawson ◽  
Judith Perlwitz ◽  
...  
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Sea Ice ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Meridional Overturning Circulation ◽  
Stratospheric Chemistry ◽  
Earth Observing System ◽  
Antarctic Sea Ice ◽  
The Antarctic

Abstract Stratospheric ozone depletion plays a major role in driving climate change in the Southern Hemisphere. To date, many climate models prescribe the stratospheric ozone layer’s evolution using monthly and zonally averaged ozone fields. However, the prescribed ozone underestimates Antarctic ozone depletion and lacks zonal asymmetries. This study investigates the impact of using interactive stratospheric chemistry instead of prescribed ozone on climate change simulations of the Antarctic and Southern Ocean. Two sets of 1960–2010 ensemble transient simulations are conducted with the coupled ocean version of the Goddard Earth Observing System Model, version 5: one with interactive stratospheric chemistry and the other with prescribed ozone derived from the same interactive simulations. The model’s climatology is evaluated using observations and reanalysis. Comparison of the 1979–2010 climate trends between these two simulations reveals that interactive chemistry has important effects on climate change not only in the Antarctic stratosphere, troposphere, and surface, but also in the Southern Ocean and Antarctic sea ice. Interactive chemistry causes stronger Antarctic lower stratosphere cooling and circumpolar westerly acceleration during November–January. It enhances stratosphere–troposphere coupling and leads to significantly larger tropospheric and surface westerly changes. The significantly stronger surface wind stress trends cause larger increases of the Southern Ocean meridional overturning circulation, leading to year-round stronger ocean warming near the surface and enhanced Antarctic sea ice decrease.

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