# Presentation: 193321

## Detecting Change in the Bering Sea Ecosystem

- Sergei Rodionov1, James E. Overland2, Nicholas A. Bond1
** ***1**JISAO, University of Washington, Seattle, WA.**2**PMEL, NOAA, Seattle, WA.*

## The SARS Method

- -2.5

- -2

- -1.5

- -1

- -0.5

- 0

- 0.5

- 1

- 1900

- 1905

- 1910

- 1915

- 1920

- 1925

- 1930

- 1910

- 5% significance level

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- RSI

- 1910

- January PDO

- Searching for the first regime shift

- SARS – Sequential Analysis of Regime Shifts

- RSI – Regime Shift Index

*l* = 10

## Searching for the next regime shift

- -1.5

- -1

- -0.5

- 0

- 0.5

- 1

- 1.5

- 2

- 2.5

- 1900

- 1905

- 1910

- 1915

- 1920

- 1925

- 1930

- 5% significance level

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- 0.7

- 0.8

- RSI

- 1910

- 1912

- 1914

- 1922

- January PDO

*l* = 10

## The North Pacific Index (Nov-Mar)1899-2003

*l* = 10

- 0.05

*p* =

- 0.1

- The North Pacific Index (Nov-Mar)1899-2003

- RSI

**1924**

**1948**

**1977**

**1924**

**1948**

**1977**

**1958**

**1989**

**2003**

## Arctic Oscillation, 1951-2003

*p = *0.05

*l* =

- 10

- 7

- 5

- 1989

- 1994

- 1996

- 1972

- 1977

## www.Beringclimate.noaa.gov

## Regime Shifts in Climatic Indices

**1943**

**1934**

**1989**

**1998**

**1976**

**1977**

- PDOa

- PDOw

- PDOs

- PDOa

- PDOs

- PDOa

- PDOs

- PDOw

- ALPI

- NPINCAR

- PNA

- NPICPC

- NPINCAR

- PDOw

- AO

- EPI

- PDOs

- EPI

- AI

- NPICPC

*p* = 10
*l*  = 0.1

## The 1989 Shift Winter (DJF) Surface Air Temperature

- The 1989 Shift Winter (DJF) Surface Air Temperature

**Notes:**
The shift of 1989 exhibited itself in a relative cooling from a very warm period of 1977-88. 

## Arctic Oscillation, Winter (DJF)

*l* = 10
*p* =  0.1

**1989**

**Notes:**
The strongest shift around 1989 occurred in the Arctic Oscillation; the index shifted from predominantly negative values before 1989 to strongly positive values after that. As the correlation map at the bottom shows, positive AO indices are associated with cooling in the Bering Sea. In the other words, much of the cooling in the Bering Sea can be attributed to the shift in Arctic Oscillation.

## Pacific Decadal Oscillation, Winter (DJF)

**1989**

*l* = 10
*p* =  0.1

**Notes:**
The PDO also had a shift in 1989 toward the lower values of the index. The average level of the index after 1989 was not as low as prior to 1977, but the shift of 1989 was still statistically significant. This negative shift in the PDO means cooling in the eastern Bering See, as this correlation map shows. 

## The North Pacific Index, Winter (NDJFM)

*l* = 10
*p* =  0.1

**1989**

## EPI

- NPICPC

- R = -0.26

- Data: 1950-2003

- 1990

- 1998

- 1990

- 1998

- R = -0.70

- Data: 1980-2003

*l* = 10
*p* =  0.1

## Correlations with SLP1950-2003

- East Pacific Index (AMJJ)

- Correlations with SLP1950-2003

- North Pacific Index (AMJJ)

**Notes:**
Both the EPI and NP indices represent a north-south dipole in SLP and the direction of the shift in 1998 suggests the enhances cyclonic activity after the shift. 

## Regime Shifts in Atmospheric Indices

*l* = 10
*p*  = 0.1

**1929**

**1938**

**1997**

**1969**

**1959**

**1977**

**1989**

- SLPw

- SATa

- SATa

- BSPI

- BSPI

- SATw

- SATa

- SLPw

- OWS

- MIX

- SATa – Annual surface air temperature, St. Paul.
- SATw – Winter surface air temperature, St. Paul
- SLPw – Winter SLP over the Bering Sea
- BSPI – Bering Sea pressure index
- OWS – Optimal wind speed for larval feeding, Mooring 2
- MIX – Summer wind mixing, Mooring 2

**Notes:**
In the atmospheric indices the shift of 1977 dominates, but the shifts of 1989 and 1997/98 are also there. 

## Mean Winter (NDJFM) SLP over the Bering Sea

- 1998

- 1989

- 1977

- 1947

- 1924

- 1911

## Mean Winter (DJFM) SAT at St. Paul

- 1998

- 1989

- 1977

- 1947

- 1924

- 1940

**Notes:**
Here is winter SAT at St. Paul, with 2 major regime shifts in 1940 and 1977. If we apply the regimes detected in slp to this temperature time series, we’ll see that generally warming occurred during cyclonic regimes and cooling during anti-cyclonic regimes, but there are exceptions. Although one can notice some cooling in the yearly 1990, it is not statistically significant. This controversy about the regime shifts around 1989 and 1998 can be seen in the oceanic indices as well.

## Regime Shifts in Oceanic Indices

**1965**

**1977**

**1983**

**2000**

- SSTPrib

- SSTPrib

- SSTM2

- ICI

- SSTPrib

- IRI

- SATPrib – Winter SST near the Pribilof Islands
- SATM2  – Winter SST at Mooring 2
- ICI   – Ice Cover Index
- IRI   – Ice Retreat Index

*l* = 10
*p*  = 0.1

- SSTM2

**1988**

**Notes:**
This is the RS index for all the oceanic time series. The shift of 1988 is not among the strongest. 

## Ice Cover Index and Surface Temperature  at Mooring 2

- ICI

- Temperature

*l* = 10
*p*  = 0.1

- 1978

- 1988

- 1977

**Notes:**
Let’s look at two indices that characterize thermal conditions in the Bering Sea: the ICI and temperature at Mooring 2, which are very well correlated overall.  Although there are more frequent cold years in the region, three very mild winters of 1996, 2001 and 2003 does not allow for determining the shift of 1989 in the ICI. This shift is somewhat more pronounced in temperature at Mooring 2.

## Regime Shifts in Biological Indices

*l* = 10
*p*  = 0.1

**1977**

**1966**

**1981**

**1984**

**1992**

**Notes:**
Unlike environmental indices, the regime shifts in biological indices are not concentrated in narrow intervals around central years. Instead it appears that different species experienced regime shifts in different years. 

## Time Series of Fish Stocks

- Herring
- year-class
- strength

- Pollock
- recruitment
- at age 1

- Bristol Bay sockeye salmon runs

- 1977

- 1989

- 1979

- 1997

- 1978

- 1989

- 1985

- 2001

*l* = 10
*p*  = 0.1

*l* = 5
*p*  = 0.1

*l* = 10
*p*  = 0.1

## Conclusions

- Characteristics of the SARS method:
- Automatic detection of regime shifts,
- Improved performance at the ends of time series,
- Can be tuned up to detect regimes of different scales,
- Can handle the incoming data regardless of whether they are presented in the form of anomalies or absolute values,
- Works well with the time series containing a trend,
- Can be applied to a large set of variables.

## Conclusions (continued)

- An application of SARS to the Bering Sea ecosystem demonstrated that
- The shift of 1977 was the strongest one in the last 50 years;
- A number of indices experienced a regime shift around 1989 (AO, PDOw, temperature at Mooring 2, herring), 1998 (PDOs, salmon), or both (NPICPC, EPI, winter SLP, flathead sole);
- The regime of 1989-1997 was characterized by a relative winter cooling and reduced cyclonic activity;
- Regime shifts in biological indices are not concentrated around certain, dominant years. The RSI values are rather evenly distributed between 1977 and 1992.