UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

§ 240.13d-2(a)

(Amendment No. 5)¹

Atlantic Power Corporation

(Name of Issuer)

Common Stock, no par value

(Title of Class of Securities)

04878Q863

(CUSIP Number)

STEVE WOLOSKY, ESQ.

OLSHAN FROME WOLOSKY LLP

1325 Avenue of the Americas

New York, New York 10019

(212) 451-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

January 10, 2018

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box ☒.

Note:  Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits.  See § 240.13d-7 for other parties to whom copies are to be sent.

1              The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

The following constitutes Amendment No. 5 to the Schedule 13D filed by the undersigned (“Amendment No. 5”). This Amendment No. 5 amends the Schedule 13D as specifically set forth herein.

Item 2 is hereby amended and restated to read as follows:

(a)       This statement is filed by:

Each of the foregoing is referred to as a “Reporting Person” and, collectively, as the “Reporting Persons.” Each Reporting Person is a party to that certain Joint Filing Agreement, as further described in Item 6. Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

Set forth on Schedule A annexed hereto (“Schedule A”) is the name and present principal business, occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted of the directors of Mangrove Master Fund, Mangrove Fund Cayman and Mangrove Capital. Mr. August is the sole director of Mangrove Partners. To the best of the Reporting Persons’ knowledge, except as otherwise set forth herein, none of the persons listed on Schedule A beneficially owns any securities of the Issuer or is a party to any contract, agreement or understanding required to be disclosed herein.

(b)       The address of the principal office of each of Mangrove Fund, Mangrove Partners, Mangrove Capital and Mr. August is 645 Madison Avenue, 14th Floor, New York, New York 10022. The address of the principal office of each of Mangrove Master Fund, Mangrove Fund Cayman and Mangrove Fund Cayman Drawdown is c/o Maples Corporate Services, Ltd., P.O. Box 309, Ugland House, South Church Street, George Town, Grand Cayman, Cayman Islands KY1-1104.

(c)       The principal business of Mangrove Master Fund is acquiring, holding and disposing of investment securities. The principal business of Mangrove Fund is investing in Mangrove Master Fund. The principal business of Mangrove Fund Cayman is investing in Mangrove Master Fund. The principal business of Mangrove Fund Cayman Drawdown is investing in Mangrove Master Fund. The principal business of Mangrove Partners is serving as the investment manager of each of Mangrove Master Fund, Mangrove Fund, Mangrove Fund Cayman and Mangrove Fund Cayman Drawdown. The principal business of Mangrove Capital is serving as the general partner of each of Mangrove Fund and Mangrove Fund Cayman Drawdown. The principal occupation of Mr. August is serving as a director of each of Mangrove Partners and Mangrove Capital.

(d)       No Reporting Person, nor any person listed on Schedule A, has, during the last five (5) years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)       No Reporting Person, nor any person listed on Schedule A, has, during the last five (5) years, been party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)       Mr. August is a citizen of the United States of America.

Item 3 is hereby amended and restated to read as follows:

The 11,469,584 Shares directly owned by Mangrove Master Fund were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in Schedule B annexed hereto (“Schedule B”). The aggregate purchase price of the 11,469,584 Shares directly owned by Mangrove Master Fund is, in U.S. dollar terms, approximately $25,690,283, including brokerage commissions.

Item 4 is hereby amended to add the following:

The Reporting Persons have had discussions with the President and Chief Executive Officer of the Issuer regarding alternative uses for the Issuer’s power plants that have expired or expiring power purchase agreements. On January 10, 2018, the Reporting Persons had a telephonic meeting with the President and Chief Executive Officer of the Issuer to discuss plans to develop and supply power to collocated data centers as well as to explore utilizing surplus power for cryptocurrency mining and other blockchain applications. The Reporting Persons also expressed interest in providing co-investment capital for such projects. These discussions are continuing.

Items 5(a)-(c) are hereby amended and restated to read as follows:

The aggregate percentage of Shares reported owned by each person named herein is based upon 115,211,976 Shares outstanding as of December 18, 2017, which is the total number of Shares outstanding as reported in the Issuer’s Prospectus filed with the Securities and Exchange Commission on December 19, 2017.

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

Percentage: Approximately 9.96%

As of the close of business on January 11, 2018, the Reporting Persons collectively beneficially owned an aggregate of 11,469,584 Shares, constituting approximately 9.96% of the Shares outstanding.

Each of the Reporting Persons, as a member of a “group” with the other Reporting Persons for purposes of Rule 13d-5(b)(1) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), may be deemed to beneficially own the securities of the Issuer owned by the other Reporting Persons. The filing of this Schedule 13D shall not be deemed an admission that the Reporting Persons are, for purposes of Section 13(d) of the Exchange Act, the beneficial owners of any securities of the Issuer he or it does not directly own. Each of the Reporting Persons specifically disclaims beneficial ownership of the securities of the Issuer reported herein that he or it does not directly own.

Item 6 is hereby amended to add the following:

On January 10, 2018 and January 11, 2018, Mangrove Master Fund entered into a series of cash-settled total return swap agreements with Morgan Stanley Capital Services LLC as the counterparty (the “Swaps”) that establish economic exposure to an aggregate of 87,370 notional Shares (the “Subject Shares”), representing less than 1% of the outstanding Shares. The Swaps provide Mangrove Master Fund with economic exposure that is comparable to the economic exposure of ownership but do not provide it with the power to vote or direct the voting of or to dispose or direct the disposition of the Subject Shares. The Reporting Persons hereby expressly disclaim beneficial ownership of the Subject Shares.

On January 12, 2018, the Reporting Persons entered into a Joint Filing Agreement pursuant to which the Reporting Persons agreed to the joint filing on behalf of each of them of statements on Schedule 13D with respect to the securities of the Issuer to the extent required by applicable law. The Joint Filing Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 7 is hereby amended to add the following exhibit:

SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: January 12, 2018

SCHEDULE A

Directors of The Mangrove Partners Master Fund, Ltd. and Mangrove Partners Fund (Cayman), Ltd.

Directors of Mangrove Capital

SCHEDULE B

Transactions in the Securities of the Issuer During the Past Sixty (60) Days

THE MANGROVE PARTNERS MASTER FUND, LTD.

Exhibit 99.1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of a Statement on Schedule 13D (including additional amendments thereto), dated the date hereof, with respect to the shares of Common Stock of Atlantic Power Corporation. This Joint Filing Agreement shall be filed as an Exhibit to such statement.

Dated: January 12, 2018