Freeze-Up Studies of the Alaskan Beaufort and Chukchi Seas: through Coastal Frontiers Corporation Vaudrey & Associates, Inc.

Transcription

1 Freeze-Up Studies of the Alaskan Beaufort and Chukchi Seas: through Coastal Frontiers Corporation Vaudrey & Associates, Inc.

2 Joint-Industry Sponsors U.S. Department of the Interior Bureau of Safety and Environmental Enforcement Shell Oil Company Statoil Petroleum AS ( )

3 Freeze-Up Studies of the Alaskan Beaufort and Chukchi Seas Topics 1. Objectives 2. Methods 3. Highlights 4. Long-Term Trends

4 Why Study Freeze-Up? 1. Design Design Ice Features (Ridges; Rubble Fields; Multi-Year Ice) Encounter Frequencies (Population; Drift Rates; Leads) Ice Encroachment 2. Construction and Operation Vessel Navigation Landfast Ice Zone (Ice Roads; On-Ice Construction) Incident Response Exploratory Drilling Season

5 Study Objectives 1. Document Ice Conditions 2. Locate and Map Significant Features Landfast Ice Zone Ice Movement Lines, Ridges, & Rubble Fields Leads & Polynyas Multi-Year Ice, Ice Islands & Icebergs 3. Locate and Characterize Ice Encroachments 4. Correlate Changes in Ice Canopy with Weather 5. Characterize Current Freeze-Up Processes and Compare with 1980s ( to )

6 Study Area: Beaufort vs. Chukchi Alaskan Beaufort Sea ESE-WNW Coastline Coast-Parallel Winds Flat Nearshore Slopes Extensive Zone of Landfast Ice Small Leads and Polynyas Beaufort Gyre Prevailing Winds Alaskan Chukchi Sea NE-SW Coastline Onshore-Offshore Winds Steep Nearshore Slopes Narrow Strip of Landfast Ice Flaw Lead Coastal Current Prevailing Winds

7 Meteorological Data Deadhorse & Barrow Ice Charts CIS & NIC Data Satellite Imagery RADARSAT-2; AVHRR; MODIS Ice Drift Buoys Shell & IABP Reconnaissance Flights Fixed-Wing & Helicopter November and February

8 Highlights MYI invasions in both basins, including first in Alaskan Beaufort Sea since First reported sighting of ice islands/icebergs in Alaskan waters since 1981 Follow-up bathymetric survey documented substantial ice gouge

9 Highlights Permanent pack ice attained historical minimum (Sep 2012) Flash freeze event in Chukchi (Oct 2012) Massive ice fracture event impacted entire Beaufort Sea (Jan Mar 2013) and produced 150-nm wide flaw lead in Chukchi

10 Beaufort Sea Ice Fracture Event on February 23, 2013 NASA, 2013

11 Long-Term Trends Air Temperatures Storms Timing of Freeze-Up Growth of First-Year Ice Development of Landfast Ice Driving Forces Responses Invasions of Multi-Year Ice

12 Air Temperature Trends Air temperatures have increased substantially since 1970s (reducing thickness of first-year ice) Largest increase has occurred in October (+9 F relative to average, delaying occurrence of freeze-up) Rate of warming has accelerated

13 Fall Storm Events Walsh and Eicken (2007): sharp rise in storm frequency during open-water & freeze-up seasons began in mid-1970s 2

14 Winter Storm Events Average: 9.4 storms/winter Average: 8.5 storms/winter (Dickens & Vaudrey, 1994) Storm Event: Daily Average Wind Speed > 15 kt (8 m/s)

15 Storm Trends Storm frequency during freeze-up has increased by about 50% since early 1980s Storm frequency in mid-winter also has increased, but only by about 10%

16 Timing of Freeze-Up in Nearshore Region Beaufort Sea 1980s: Oct 4 (Vaudrey, ; ) : Oct 25 Chukchi Sea Mid-1970s: Early October (Mahoney, et al., 2007) : Nov 20

17 Trends in Timing of Freeze-Up Beaufort Sea: Currently occurs during fourth week in October Standard deviation = 8 days ~3 weeks later than in 1980s Chukchi Sea: Currently occurs during third week in November Standard deviation = 10 days Nearly one month later than in Beaufort At least one month later than in 1970s

18 First-Year Ice Growth Computed Thickness of First-Year Ice through : 171 cm through : 152 cm Net Change: -19 cm (Thickness computed using method of Lebedev based on FDD measured at Barrow Airport)

19 First-Year Ice Growth Brown & Cote (1992): insulating effect of increased snowfall outweighs warmer air temperatures in reducing ice thickness Trend: +2.4 cm/year Data from Barrow Airport 1

20 Trends in First-Year Ice Growth Based on temperature alone, first-year ice thickness has decreased by more than 11% (19 cm) since early 1980s Increased snowfall may be causing an even greater reduction in thickness due to its insulating effects Other temperature-related effects, including reduced ice production in leads, decreased consolidation of ridges, and reduced ice strength, probably exert greater impacts on ice dynamics than reduced ice thickness

21 Trends in Landfast Ice Beaufort Sea West of Prudhoe Bay: LFI is similar to that in 1980s, but develops more slowly East of Prudhoe Bay: LFI not only develops more slowly, but is less likely to remain stable due to inadequate grounding Chukchi Sea Narrow, ephemeral LFI zone observed in 1980s continues to prevail today

22 Multi-Year Ice Invasions Beaufort Sea 1980s: 3 of 6 winters through : 1 of 9 winters through : 1 of 7 winters Chukchi Sea 1980s: 3 of 3 winters through : 5 of 9 winters through : 6 of 7 winters

23 Trends in Multi-Year Ice Invasions: Beaufort Sea Probability of large MYI floes invading nearshore region has decreased to ~13% (2 of past 16 winters) Causes Amount of MYI has decreased Ice edge has retreated farther north in summer Open-water season has become warmer & stormier

24 Trends in Multi-Year Ice Invasions: Chukchi Sea Probability of large MYI floes invading nearshore region has decreased to ~69% (11 of past 16 winters) Impacts of less MYI, ice edge retreat, warmer temperatures & increased storminess have been partially offset by two phenomena: Multi-Year Gateway 9 of past 16 winters Early-Season Entry 3 of past 16 winters Common Feature Loss of confinement

25 Chukchi Sea Flaw Lead (January 22, 2013) Flaw Lead Point Barrow Icy Cape After: National Weather Service, 2013

26 Multi-Year Gateway (December 29, 2015) Extended Flaw Lead Multi-Year Ice Multi-Year Ice Southern Boundary Icy Cape Harrison Bay After: National Weather Service,

27 Early-Season Entry (Nov 16, 2015) Early- Season Entry Multi-Year Ice Edge Crackerjack Prospects Hanna Shoal Prospects Burger Prospects Devil s Paw Prospects After: RADARSAT-2 Data and Products MacDonald Dettwiler and Associates Ltd., 2015 All Rights Reserved 1

28 Conclusions and Recommendations 1. Ice conditions have changed substantially since 1980s, particularly during early freeze-up 2. Many design & operational criteria derived from data obtained in the 1980s are obsolete, including: Length of open-water season Thickness of first-year ice Encounter frequencies with design features 3. Multi-year ice, ice islands & icebergs remain key design considerations, particularly in Chukchi 4. The next frontier: break-up First investigation in Spring 2017

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30 14-m Pile-Up with 27-m Encroachment Flaw Lead Wake Northstar Production Island, January 2008

31 RADARSAT-2 Image (February 15, 2016) Multi-Year Ice Edge Multi-Year Ice Floe 25 x 48 km Landfast Ice Edge After: RADARSAT-2 Data and Products MacDonald Dettwiler and Associates Ltd., 2016 All Rights Reserved

32 Multi-Year Ice Floes in Beaufort & Chukchi Seas Chukchi Sea: February 9, 2010 Western Beaufort Sea: February 7, 2010

33 40-m x 80-m Grounded Iceberg in Chukchi Sea Flaw Lead Wake February 6, 2012

34 Ice Gouge Incised by Iceberg 0.5 km Water Depth: 30 m June 30, 2012 Max Incision Depth: Incision Width: 4.15 m 27 m Length: 2 km