Argo world 

What Is Polar Argo?

Argo floats have been successfully deployed in the seasonal ice zone of both poles over the past decade. More than 45,000 profiles south of 60°S have been collected since 2001. Advances in float technology including two-way communications through the Iridium satellite network, software modifications (ice avoidance algorithm and the ability to store winter profiles) and improved hardware have resulted in ice floats surviving multiple winters under sea ice.

In recognition of the successful deployment of floats into the seasonal ice zone and the desire for a truly global Argo data system, the Argo Steering Team has recommended that core Argo be extended beyond 60°S and 60°N. In order to do this, the community must find additional resources to ensure the sustainability of the core array and support the extensions into the high latitudes.

The ice-avoidance algorithm is essential for ice floats and has been well established for the Southern Ocean. Manufacturers have integrated it into their software and are offering it free of charge with the float purchase. Therefore an ice float in the Southern Ocean and the Nordic Seas costs the same as a regular open ocean float. Adaptations to the ice-avoidance algorithms have been performed in pilot studies in the more heavily ice-covered areas in northern hemisphere and algorithms have successfully been integrated in the float types deployed in the Baffin Bay and the Chuckhi Sea. The failure rate in the Southern Ocean and Nordic Seas is slightly higher overall (20-30%) due to the increased risk of damage through encounters with ice. Plans to re-seed ice floats in the Polar Regions should take into account the slightly lower overall life expectancy.

Special ice pilot studies are underway in the Arctic and in many sectors of the Antarctic. Floats equipped with biogeochemical (BGC) sensors, floats with acoustic RAFOS sensors for under-ice geolocation, deep bottom-following floats on the Antarctic slope and floats deployed on the Antarctic continental shelf are all extending the boundaries of what's possible for Polar Argo.

All photos courtesy of SOCCOM
Some photos also courtesy of Isa Rosso
Polar Argo Design
Technology challenges
Pilot arrays
Links to related pages
Task team leads

Polar Argo Design

The number of floats required to extend the core Argo array beyond 60°S and 60°N was estimated by developing a 3 x 3° grid over the global oceans and finding grid cells (with a depth of 2000m or greater) in the Southern Ocean, or 1000m or greater, in the Arctic Ocean. The grid cells that are ice free in summer were identified by mapping the median ice extent limit (1979-2000) from the NOAA National Ice Centre data. The density coefficient of floats per grid cell is x1.

This results in a target number of floats of 326 in the Southern Ocean (orange cells in map below) and 141 in the Arctic Ocean (grey cells in the map below).

Taking into account partial grid cells with depths greater than 2000 m for the Southern Ocean yields a slightly higher target of 360 active floats (including 85 RAFOS-equipped floats in the Weddell Sea and 110 floats in the Ross Gyre).

This analysis does not take into account the shrinking summer ice extent in the Arctic. It should be noted that in the Arctic proper, a mix of platforms will be required (i.e. both Argo floats and ice tethered profilers) to better deal with expected multi-year ice conditions in the Central Arctic. In the Central Arctic an observing system has been installed within the French framework "Observatoire Français de l'Arctique" which is based on ice tethered floats which collect real time simultaneous observations of the ocean, the sea ice, the snow and the atmosphere. The network consisting of 15 stations covers mainly the Beaufort Gyre and the Arctic transpolar drift. The deployment has started back in 2012 in the IAOOS project and is financed for a 7 year period so far. It should also be noted that large areas in the Arctic are within territorial waters and will require increased international cooperation in order to reseed floats.

The map below shows how well we are meeting the design goals for Argo. Blue areas indicate regions that are undersampled and where gaps in the array are likely to develop. Conversely, red areas indicate regions that are well sampled. The polar oceans in both hemispheres are currently under-sampled with substantial gaps opening up in the southernmost sectors of the Southern Ocean and in parts of the Arctic.


Technology challenges

Iridium two-way communication is essential for ice floats as well as the ability to internally store profiles over winter when the float cannot surface due to ice cover. When the sea ice first melts in spring the float will surface and telemeter all of the stored under-ice profiles from the previous winter period, however the profile position data are lost. A challenge for the community is how to best estimate float positions when the float is under ice. A number of efforts are underway to improve estimation of under-ice profile location.

Ice floats in the Weddell Sea that are equipped with a RAFOS receiver can be geolocated through an array of acoustic moorings. Through the analysis of received acoustic signals the position data can be calculated in post processing. A proposal to deploy an acoustic array of sound sources and RAFOS-equipped floats is under consideration for the Ross Sea.

Active ice sensing is being tested on the Pro-Ice floats deployed in the Baffin Bay. All floats carry an upward-looking altimeter to detect ice-conditions and one float was additionally equipped with an optical ice detector and was tested in May 2014 under the floe at Qikiqtarjuaq with the sailing ship Vagabond as basecamp. Optical ice detection uses the light depolarizing properties of sea ice and tries to discriminate between different layers of ice. Based on the analysis of these data, further adaptions to the ice-sensing algorithm will be performed.

Another challenge is to minimize potential damage to the floats surfacing in partially ice covered conditions. To avoid shocks from contact with the ice, some float have an additional cage at the top which protects the CTD, any additional sensors and strengthened antennas.


Southern Ocean Ice Argo - floats south of 60°S

Ice floats from the early 2000's had a higher failure rate and lower life expectancy with approximately 40% achieving 100 cycles and just 15% reaching 200 cycles. Iridium APEX ice floats (mostly deployed since 2010) have very good survivability and lifetimes, with 90% achieving 120-200 cycles (comparable to regular floats).

The two figure panels below show the number of profiles observed south of 60°S from Argo floats (between 2000-2016) on the left and those returned from ship-board hydrography (1900-2013) on the right. In just 16 years, more than 45,000 profiles have been collected by Argo floats including 20,000 winter profiles, this can be compared to 2,700 winter profiles available from ships.

Twenty four percent of profiles south of 60°S are under ice (black dots). The open water profiles are indicated by green dots. The growth of the Southern Ocean array has currently stalled at around 40% of the required number of operational floats.

The ice Argo community always welcomes contributions of floats for the Southern Ocean array. We are able to assist countries that are new to Argo to partner with countries that have expertise and deployment opportunities in the Southern Ocean.

Left hand figure shows profiles from Argo floats between 2000 - 2016 south of 60°S.
Right hand figure shows profiles from ship-board hydrography between 1900 - 2013 south of 60°S.


Acoustically-tracked RAFOS floats in the Weddell Sea

An array of acoustically-tracked floats equipped with RAFOS receivers is operational in the Weddell Sea. The array of acoustic sound sources (with an effective range of around 500km) is maintained by the Alfred-Wegener Institute in Germany. The correlation height depends primarily on distance between the float and the sound source but also strongly on season. In summer, there are large correlation heights for distances up to 700km, which decreases to 300km in winter, mainly due to differences in stratification in the upper water column and interference from sea ice (Klatt et al., 2007). However, poorer signals can still be used if they match up with higher correlation heights, resulting in an effective year-round range of approximately 500km (Klatt et al., 2007).

Upper panel: Correlation heights of RAFOS floats in the Weddell Sea.
Lower panel: Trajectories of five acoustically-tracked RAFOS floats at 750m depth in the Weddell Sea between December 2002 and February 2004, (figure from Klatt et al. (2007)
http://journals.ametsoc.org/doi/pdf/10.1175/JTECH2026.1


Pilot Arrays

Southern Ocean Pilots: Wilkes Land, East Antarctica

Results from an array of ice Argo floats deployed under sea ice off the Wilkes Land Coast of Antarctica are highlighted in a paper by Annie Wong and Steve Riser, Journal of Physical Oceanography, 2011.

The seasonal cycle of the upper 500m of the ocean is shown below in a vertical section from a float that survived for two winters.

http://flux.ocean.washington.edu/riser_web/wong.riser.robertson.land.pdf


The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program

The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program is a six-year initiative funded by the NSF's Division of Polar Programs, with additional support from NOAA and NASA, headquartered at Princeton University, launched in September 2014. SOCCOM's mission is to drive a transformative shift in understanding of the role of the Southern Ocean in climate change and biogeochemistry. SOCCOM is deploying ~200 ice-capable biogeochemical profiling floats throughout the Southern Ocean, contributing to the core Argo program with additional floats and sensors. The floats provide a profile every 10 days of temperature, salinity, nitrate, oxygen, pH, optical backscatter, and chlorophyll fluorescence to 2000 m depth. These observations are being assimilated in an ocean model, the Southern Ocean State Estimate, which provides high quality air-sea flux "reanalysis" specific to the Southern Ocean, and dynamically consistent interpolation of the observations. Using this observational data and the state estimate output, high resolution earth system models are being improved to both increase our understanding of the Southern Ocean's current workings and make better projections of the future trajectory of the Earth's climate and biogeochemistry.


Plot of SOCCOM float locations. Photo courtesy of Isa Rosso


Arctic floats north of Lomonosov Ridge

A research initiative called SODA (Stratified Ocean Dynamics in the Arctic) is aiming to deploy ~20 floats in the area of the Beaufort Gyre. It has been implemented recently in 2016 and is planned for a 5 year period unti 2015. A persistent loss of sea ice volume can be anticipated from the observed decrease in sea-ice extent and decreasing ages of the ice. The aim of SODA is therefore to understand these changes and their impact on arctic stratification and circulation, sea ice evolution, and the acoustic environment.

The trajectory of one of the floats deployed in 2016 is shown in the figure. Although the float was deployed in rather shallow water initially, and worked in an ice pack for a decent amount of time it has operated for 147 cycles and monitored the multi-layer structure of temperature field in the Arctic over the shelf as well as the shelf break.

http://argo.whoi.edu/alamo/9058/index.html


Arctic floats in the Baffin Bay

Baffin Bay has been selected as a preferred area for studying ice-edge phyto-plankton blooms in high latitudes. Climate change seems to affect these blooms and observations by Ocean Remote Sensing show that the spring blooms occur now 50 days earlier than in 1997. Deployment of PRO-ICE floats in the Baffin Bay has started in 2015 and will continue until 2020 as a cooperation between the French program NAOS and the Canadian program FCI. Altogether 19 floats are planned with funding for 10 floats from France and 9 floats from Canada. The floats carry a bio-geochemical payload including sensors for oxygen, nitrates, light measurements at different wavelength, chlorophyll-a, CDOM and backscattering.

Courtesy of Marcel Bain and Claudie Marec

First field tests have demonstrated the challenges of having a float surface under these environmental conditions. An ice layer as thin as 2 cm can prevent the float from surfacing, since it only has a pull of ~ 500-600 g when ascending.

The adaption of the ISA developped by Klatt et al (2007) to the hydrographic conditions of the Baffin Bay has resulted in an appropriate choice of a temperature threshold which differs from the one selected for the Southern Ocean.

Courtesy of E. Leymaire LOV

In summer 2016, 5 PRO-Ice were deployed during the cruise "Greenedge" onboard the Canadian icebreaker Amundsen. 4 floats were deployed in Baffin Bay and the 5th in the Labrador Sea.

Deployment of the four Pro-Ice floats on July 9th 2016:
takapm009B (WMO 6902667), lat 69°30.062'N / Long 60°08.815'W
takapm013B (WMO 4901802), lat 69°30.029'N / Long 61°00.658'W
takapm05B (WMO 4901803), lat 69°19.341'N / Long 60°58.997'W
takapm014B (WMO 6902668), lat 69°20.209'N / Long 60°13.251'W.

Routes of the 4 floats in Baffin Bay since their deployment until 2016, November 1st were they navigate in a winter pattern (profile down to 1000m and rise to 15m under the surface). On the map, the shape of the floats represents the position where the floats were deployed in Summer 2016.

Examples of time series data from GreenEdge PRO-ICE floats

7 PRO-ICE will be deployed in Baffin Bay in summer 2017, during the Arcticnet cruise onboard the Canadian icebreaker Amundsen.


Links to related pages

IAOOS: Ice - Atmosphere - Arctic Ocean Observing system: http://iaoos.ent.upmc.fr/en/index.html

NAOS: Novel Argo Ocean Observing System: http://en.naos-equipex.fr/

MEOP: Marine Mammals Exploring the Oceans Pole to Pole: http://www.meop.net/

SOCCOM: The Southern Ocean Carbon and Climate Observations and Modeling program: http://soccom.princeton.edu/

SODA: Stratified Ocean Dynamics in the Arctic: http://www.apl.washington.edu/project/project.php?id=soda

WAPITI - special ice pilot study using Argo ice floats (and seals, ship-based data and models) to investigate the large-scale dynamics of the Weddell Sea: http://wapiti-project.com/


Task team leads

The Polar Argo Task Team is comprised of:

Birgit Klein (Southern Ocean, SOARC)
Esmee van Wijk (Southern Ocean, SOARC)
Steve Riser (Southern Ocean)
Steve Rintoul (Southern Ocean)
Steven Jayne (Arctic, ALAMO)
Olaf Boebel (Southern Ocean, RAFOS, Weddell)
Matt Donnelly (SOARC)
Lynne Talley (Southern Ocean, SOCCOM)
Marcel Babin (Arctic, PRO_ICE)
Claudie Marec (Arctic, PRO-ICE)
Jean-Baptiste Sallee (WAPITI, Southern Ocean)
Christine Provost (ITP, IAOOS)