<SUBMISSION>
<ACCESSION-NUMBER>0001104659-13-029485
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20130228
<FILING-DATE>20130415
<DATE-OF-FILING-DATE-CHANGE>20130415
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>Ronan Terrence
<CIK>0001557506
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-34691
<FILM-NUMBER>13762379
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>ONE FEDERAL STREET 30TH FLOOR
<CITY>BOSTON
<STATE>MA
<ZIP>02110
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>ATLANTIC POWER CORP
<CIK>0001419242
<ASSIGNED-SIC>4900
<IRS-NUMBER>550886410
<STATE-OF-INCORPORATION>A1
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>ONE FEDERAL STREET
<STREET2>FLOOR 30
<CITY>BOSTON
<STATE>MA
<ZIP>02110
<PHONE>617-977-2400
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>ONE FEDERAL STREET
<STREET2>FLOOR 30
<CITY>BOSTON
<STATE>MA
<ZIP>02110
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>a4.xml
<DESCRIPTION>4
<TEXT>
<XML>
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<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-02-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001419242</issuerCik>
        <issuerName>ATLANTIC POWER CORP</issuerName>
        <issuerTradingSymbol>AT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001557506</rptOwnerCik>
            <rptOwnerName>Ronan Terrence</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ATLANTIC POWER CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>ONE FEDERAL ST., FLOOR 30</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02110</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive Vice President-CFO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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                <value>Common Shares</value>
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                    <value>3120</value>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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                <directOrIndirectOwnership>
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            <transactionAmounts>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
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        <nonDerivativeTransaction>
            <securityTitle>
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                <footnoteId id="F2"/>
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            <transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
                    <value>3413</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares</value>
                <footnoteId id="F2"/>
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            <transactionDate>
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            <transactionCoding>
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                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
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                    <value>667</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.85</value>
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                </transactionAcquiredDisposedCode>
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                    <footnoteId id="F5"/>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Notional Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
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            <transactionDate>
                <value>2013-02-28</value>
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            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3120</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.33</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3120</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>10240</value>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Notional Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F4"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-04-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6000</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.85</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10240</value>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Notional Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F4"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-04-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.85</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F4"/>
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            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10240</value>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person acquired shares pursuant to the vesting (disclosed on Table II) of notional shares awarded in 2012. Two thirds of the vested notional shares were settled in common shares and one third were settled in cash, net of applicable tax withholding.</footnote>
        <footnote id="F2">The reporting person acquired shares pursuant to the vesting (disclosed on Table II) of notional shares awarded in 2013. Two thirds of the vested notional shares were settled in common shares and one third were settled in cash, net of applicable tax withholding.</footnote>
        <footnote id="F3">The reporting person vested in respect of one-third of the notional shares granted in 2012 (including additional notional shares accrued pursuant to dividend equivalent rights).</footnote>
        <footnote id="F4">Represents a grant of notional shares pursuant to the Company's Long-Term Incentive Plan (&quot;LTIP&quot;) in 2013 that vest ratably with respect to one-third on each of April 11, 2013 (the grant date), February 28, 2014 and February 28, 2015. Under the LTIP, each notional share represents a right to receive one-third in cash (net of any applicable withholdings) and the remainder in a fractional common share, or (at the election of the reporting person) one common share, or (at the discretion of the board of directors of the Company) cash only.</footnote>
        <footnote id="F5">The amount of securities beneficially owned following the reported transactions reflect those holdings as of the date of this Form.</footnote>
        <footnote id="F6">The total includes dividend equivalent rights accrued on the notional shares previously earned pursuant to the LTIP. Dividend equivalent rights are credited in notional shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Barry E. Welch, attorney-in-fact</signatureName>
        <signatureDate>2013-04-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
